ATOLL RESEARCH BULLETIN No. 143
THE SAFE USE OF OPEN BOATS IN THE CORAL REEF ENVIRONMENT
by S. B. Domm
Issued by
THE SMITHSONIAN INSTITUTION Washington, D. C., U. S. A.
February 16, 1971
THE SAFE USE OF OPEN BOATS IN THE CORAL REEF ENVIRONMENT
by S. B . Domm
INTRODUCTION
For t h e p a s t two and a h a l f y e a r s I have been employed a t Heron I s l a n d Research S t a t i o n , Great B a r r i e r Reef of A u s t r a l i a . The work has e n t a i l e d much time i n s m a l l , open b o a t s i n many weathers. Often it was n e c e s s a r y t o t r a v e l t o r e e f s up t o twenty m i l e s away. Diving, c o l l e c t i n g , and surveying o f t e n meant u s i n g b o a t s i n c o n d i t i o n s t h a t were p o t e n t i a l l y hazardous.
Small b o a t s a r e a v a i l a b l e at t h e Research S t a t i o n and, of t h e s c i e n t i s t s t h a t o c c a s i o n a l l y u s e them, few have any p r a c t i c a l exper- i e n c e i n such m a t t e r s , y e t more and more s c i e n t i s t s a r e f i n d i n g i t n e c e s s a r y t o r e l y on themselves. I have seen t h e most i n t e l l i g e n t academics make i n c r e d i b l e b l u n d e r s when u s i n g b o a t s , b l u n d e r s t h a t i n s l i g h t l y d i f f e r e n t circumstances could have had s e r i o u s conse- quences.
I t i s my hope t h a t t h e s e n o t e s w i l l provide u s e f u l information f o r t h o s e s c i e n t i s t s working i n t h e c o r a l r e e f environment. Although w r i t t e n e s p e c i a l l y with t h e Great B a r r i e r Reef of A u s t r a l i a i n mind, t h i s i n f o r m a t i o n should prove u s e f u l elsewhere.
BOATS SUITABLE FOR CORAL REEF WORK
For working around c o r a l r e e f s a b o a t should b e b o t h maneuver- a b l e and of shallow d r a f t . Light weight i s a l s o an advantage, except p o s s i b l y i n a boat used only f o r d i v i n g . When working on a s m a l l i s l a n d t h a t r e c e i v e s l i t t l e p r o t e c t i o n from i t s surrounding r e e f it i s o f t e n an advantage t o b e a b l e t o p u l l one's b o a t w e l l up on t h e beach ( u s u a l l y with t h e h e l p of a rubber r o l l e r ) , s i n c e such p l a c e s o f f e r few p o s s i b i l i t i e s f o r a s a f e anchorage. A l i g h t b o a t i s a l s o v e r y u s e f u l i n t h a t it can b e "walked" over t h e r e e f c r e s t , e t c . when water i s very s h a l l o w . However a l i g h t l y loaded aluminum b o a t i s v e r y s u b j e c t t o t h e wind, and can be blown along a t a
s u r p r i s i n g speed. This can prove v e r y troublesome a t t i m e s , e s p e c i a l l y when one i s t r y i n g t o row.
I have had t h e most experience w i t h aluminum b o a t s and have found them t o be q u i t e s a t i s f a c t o r y . They a r e q u i t e l i g h t and y e t s t r o n g and capable of c a r r y i n g v e r y heavy l o a d s . A v e r y good b o a t i s t h e
17'6" DeHavilland "Hercules" which when powered by a 40 hp outboard motor i s capable o f c a r r y i n g l a r g e loads i n rough s e a s and y e t when
l i g h t l y loaded i s f a s t and q u i t e maneuverable. Another aluminum b o a t I have had much experience with i s t h e 12 f o o t DeHavilland "Sea Otter".
Powered by a 10 hp. outboard motor it w i l l c r u i s e n i c e l y a t about 12 k n o t s with 2 persons p l u s g e a r . Even w i t h a good load both t h e s e b o a t s w i l l r e t a i n enough f r e e b o a r d t o b e r e l a t i v e l y s a f e i n rough s e a s .
There a r e many o t h e r d i f f e r e n t makes of aluminum b o a t s , a l l having advantages and disadvantages.
Although I do n o t recommend outboard motors f o r every use they appear t o be i d e a l f o r work around c o r a l r e e f s . A b o a t powered by an outboard engine i s v e r y maneuverable, e s p e c i a l l y i f l i g h t l y loaded.
This enables one t o approach v e r y c l o s e t o a r e e f o r t o t h r e a d o n e ' s way through t h e p a t c h r e e f s of a lagoon. I t a l s o makes l o a d i n g o r unloading passengers o r equipment onto a r e e f e a s i e r . Experience with s i z e s o f up t o 40 hp. has proven t o me t h a t an Evinrude outboard motor can be a r e l i a b l e and very v e r s a t i l e e n g i n e . An outboard motor can be removed e a s i l y from t h e b o a t , making i t l i g h t e r f o r h a u l i n g up on t h e beach o r on board a s h i p . I t can be exchanged between one b o a t and another, i s r e a d i l y t i l t e d up when i n shallow water o r a t anchorage, and can even be run f o r s h o r t d i s t a n c e s i n a s e m i - t i l t e d p o s i t i o n i f power i s necessary i n v e r y shallow w a t e r . A s h e a r o r d r i v e p i n , o r even a p r o p e l l e r can b e r e p l a c e d q u i c k l y and e a s i l y . One major
disadvantage of any outboard motor i s t h e h i g h r a t e of f u e l consumption.
On occasion I have used two outboard motors, a l a r g e one f o r t r a v e l i n g from one r e e f t o another, and then a s m a l l e r ( e . g . 5 hp) one f o r going over a r e e f o r when prolonged slow running i s n e c e s s a r y ( e . g . echo sounder s u r v e y s ) . The l i g h t weight and r e l i a b i l i t y o f t h e modern outboard makes it v e r y u s e f u l indeed.
A n o t e on s t e e r i n g systems i s a p p r o p r i a t e s i n c e f r o n t s t e e r i n g by means of a s t e e r i n g wheel i s becoming more p o p u l a r . There appear t o be advantages and disadvantages t o both methods. Generally I p r e f e r t h e s i m p l e r method of s t e e r i n g d i r e c t l y and t h e r e i s much l e s s o f t h e unpleasant "pounding" i n t h e s t e r n than up forward, however i t i s u s u a l l y much w e t t e r . With wheel s t e e r i n g t h e motor cannot be t i l t e d s o r e a d i l y n o r motors exchanged s o e a s i l y . A l i g h t l y loaded b o a t can pound i n a most unpleasant manner up forward i n a s h o r t , s t e e p s e a . E l e c t r i c s h i f t s , s t e e r i n g c a b l e s , e t c . reduce t h e o v e r a l l r e l i a b i l i t y o f any b o a t . The s t e e r i n g wheel up forward on t h e o t h e r hand i s much l i k e d r i v i n g a c a r , g i v e s b e t t e r v i s i o n i n f r o n t and i s u s u a l l y much d r i e r when t r a v e l i n g a t high speed.
Various designs o f j e t p r o p e l l e d b o a t s p l u s t h e a l r e a d y p o p u l a r
inboard-outboard may prove very u s e f u l f o r work on c o r a l r e e f s . Generally
an inboard engine (especially d i e s e l ) i s more r e l i a b l e and more
economical t o run than an outboard; however most a r e heavier and more expensive than an outboard.
TIDES
The t i d e s of t h e Great B a r r i e r Reef of A u s t r a l i a a r e semi-diurnal, and unlike many c o r a l r e e f areas of t h e world t h e r e i s here a marked t i d a l range. In t h e southern p a r t of t h e Reef t h e range i s over 8 f e e t , elsewhere i t can be much g r e a t e r .
I t i s of t h e utmost importance f o r s c i e n t i s t s working around c o r a l r e e f s t o have t i d e t a b l e s (which may need t o be adjusted f o r o u t e r r e e f a r e a s ) , and t o know t h e s t a t e of t h e t i d e . I f t i d e t a b l e s a r e not available, i t i s an easy matter t o determine t h e time of e i t h e r low o r high t i d e by marking t h e beach as t h e water advances o r recedes.
Knowing t h a t t h e t i d e changes every 6 hours and t h a t t h e time of t h e t i d e advances each day by approximately 50 minutes, one can approximate t h e time of any t i d e f o r days i n advance.
I t w i l l save much trouble and p o s s i b l e damage t o one's boat t o mark out across t h e reef a channel c l e a r of niggerheads, by d r i v i n g poles i n t o t h e r e e f o r e r e c t i n g markers o f some kind. This w i l l i n d i c a t e when t h e water i s s u f f i c i e n t l y deep t o enable a boat t o come and go s a f e l y . On many r e e f s t h e lee, e s p e c i a l l y t h e western end, gives t h e b e s t approach t o an i s l a n d o r r e e f .
During t h e time I have worked a t Heron Island I have seen many f o o l i s h mistakes made regarding t h e t i d e s . I t should be obvious t h a t i f one d e s i r e s t o do any work on t h e r e e f f l a t without diving, one must plan h i s v i s i t t o coincide with a low s p r i n g t i d e , when most of t h e r e e f f l a t w i l l be exposed f o r about 3 hours (water only a few
inches deep). I t i s a l s o important t o note t h a t t h e height of t h e t i d e s i s not even; of t h e two highs i n 24 hours one i s higher than t h e o t h e r . For example, during t h e summer t h e lower of t h e two low t i d e s occurs during t h e n i g h t .
Spring t i d e s (having t h e g r e a t e s t range) occur twice each month, coinciding very closely with t h e new and f u l l moons. The height of any t i d e can be a f f e c t e d by t h e wind; t h e wind can p i l e water up on a r e e f o r it can speed up t h e drainage of water from a r e e f f l a t . On a low s p r i n g t i d e t h e r e w i l l usually be very l i t t l e water on t h e r e e f f l a t from approximately one hour before u n t i l two hours a f t e r t h e time of low water, giving a maximum of 3 hours working time. When working i n an enclosed lagoon one must be very c a r e f u l not t o get "trapped" i n t h e lagoon by a f a l l i n g t i d e .
For underwater photography t h e neap t i d e s a r e often t h e b e s t as v i s i b i l i t y i n t h e water i s b e t t e r then.
Tidal Stream
This aspect of t h e t i d e s i s o f t e n not s o apparent as t h e v e r t i c a l movement and v a r i e s both i n i n t e n s i t y and d i r e c t i o n . The t i d a l stream i s usually c a l l e d a c u r r e n t , and on t h e Great B a r r i e r Reef it changes i t s d i r e c t i o n with the change of t i d e . The highest v e l o c i t y occurs with the spring t i d e s and v a r i e s from 2 t o 7 knots.
Information regarding t h e t i d a l stream can be found i n t h e
Australian P i l o t , S a i l i n g Directions, o r o t h e r n a u t i c a l publications, and i s usually p r i n t e d on c h a r t s using arrows t o i n d i c a t e d i r e c t i o n s . I f one works on uncharted r e e f s it may be a good idea t o find out t h e d i r e c t i o n s of t h e currents by t h e use of dyes. This information may influence one's choice of a work area. The wind can modify t h e s t r e n g t h o r even the d i r e c t i o n of a t i d a l stream, and it i s p o s s i b l e t h a t
during neap t i d e s a s t r o n g wind blowing against t h e stream may even reverse i t s flow. I t i s o f t e n necessary t o time one's a c t i v i t i e s t o coincide with t h e weakest t i d a l stream. Any c o l l e c t i n g w i l l be affected by t h e s t r e n g t h and d i r e c t i o n of t h e current, e s p e c i a l l y when working i n a channel between r e e f s , o r on t h e windward o r f r o n t of a r e e f . When working j u s t o f f a r e e f i t i s easy t o pick out s w i r l s , o r eddies of t h e t i d a l stream ( t i d a l r i p ) as i t flows p a s t t h e r e e f and often the i n t e r f a c e between t h e two bodies o f water i s very sharply defined. Generally t h e l e e of a long r e e f i s l e s s affected by t h e t i d a l stream than t h e more windward a r e a s . The stream i s often
f e l t on the r e e f f l a t during high t i d e s .
A very important aspect of t h e t i d a l stream i s t h a t when it i s flowing against t h e wind, a very s t e e p and unpleasant sea can develop.
This i s e s p e c i a l l y c h a r a c t e r i s t i c of channels between adjacent r e e f s , o r over very shallow a r e a s . When t r a v e l i n g between r e e f s i n an open boat with a wind blowing one should endeavor t o choose t h e time when
the t i d a l stream i s favorable.
APPROACHING AND GOING OVER A REEF
To s a f e l y approach and go over a r e e f depends on being able t o see the margin of t h e r e e f , and on knowing how much water covers it.
With a high spring t i d e it should be possible t o go over a r e e f j u s t about anywhere, except on t h e windward s i d e s of many exposed r e e f s where t h e r e a r e o f t e n l a r g e niggerheads, some of which may be over 5 f e e t high. The niggerheads u s u a l l y occupy a r a t h e r narrow zone within approximately 100 yards of the outer r e e f margin. This zone should be navigated with caution! Often the niggerheads occupy t h e highest p a r t of the r e e f ( r e e f c r e s t ) , which adds t o t h e i r danger.
Proper use of t i d e t a b l e s and d i r e c t observation of water depth w i l l enable one t o a s c e r t a i n whether or not t h e r e i s s u f f i c i e n t water t o go over a r e e f . I t i s a l s o important t o note t h a t a l l r e e f s a r e not
of t h e same height, and t h a t even on one r e e f t h e windward a r e a i s usually higher than t h e l e e .
And now f o r t h e most important aspect of r e e f navigation near a reef--being able t o see i t ! During good conditions a r e e f i s very easy t o see, t h e higher t h e observer t h e f a r t h e r away a r e e f can be seen. From about one mile one can usually see t h e breaking s u r f ,
e s p e c i a l l y on t h e windward s i d e a s viewed from t h e l e e . With any swell running t h i s can be depended upon t o i n d i c a t e t h e presence of a r e e f . As one c l o s e l y approaches a r e e f , marked c o l o r differences w i l l become
apparent; t h e deep blue of deep water changing t o t h e green of shallow water and then t h e brown of t h e r e e f below t h e surface. Unfortunately these colors a r e only apparent under t h e following conditions: sun r e l a t i v e l y high i n t h e sky and a t l e a s t a gentle breeze d i s t u r b i n g t h e surface of t h e water. Therefore, during e a r l y morning and l a t e evening, with an overcast sky o r during a dead calm, a r e e f becomes almost impossible t o see except by t h e presence of s u r f breaking o r thhe presence of a t i d e r i p . From t h e above it i s obvious t h a t any s c i e n t i s t t r a v e l i n g around an unfamiliar r e e f should do s o only during optimum conditions. Traveling a t n i g h t except i n a very f a m i l i a r a r e a can be extremely dangerous.
When going over a r e e f one should proceed slowly, watching f o r t h e brown patches t h a t might represent niggerheads. I f t h e r e i s some
uncertainty regarding t h e depth of water one should go very slowly, s w i m i n and t e s t t h e water, t i l t t h e motor and row t h e boat across, run t h e boat across with the motor s e m i - t i l t e d , o r i f t h e wind i s favorable, j u s t l e t it blow one across. When leaving a lagoon on a f a l l i n g t i d e one can often use t h e current of escaping water t o d r i f t across t h e reef c r e s t i f t h e depth i s i n s u f f i c i e n t t o use the motor. I f one i s working extensively i n a lagoon o r over a r e e f f l a t it i s very u s e f u l t o use a small, shallow d r a f t outboard motor.
Avoid a breaking s u r f a t a l l c o s t s , even t h e swell surging up on a r e e f during low t i d e on a calm day i s p o t e n t i a l l y dangerous.
Windward and leeward approaches t o a r e e f
The l e e of a r e e f i s t h e s a f e s t place t o e i t h e r work o r land from a boat. During low t i d e , a r e e f i s i n e f f e c t a very good breakwater, with calm water behind it. Ideal conditions f o r landing a r e a wind blowing off t h e r e e f and a sea with p r a c t i c a l l y no swell ( t h i s may never occur!). A t such a time one can bring t h e bow of t h e boat up t o a
s o l i d looking outcrop of t h e r e e f very slowly, and with one person holding t h e boat, t h e others can get out. The anchor can be put on top of t h e r e e f and t h e wind w i l l hold t h e boat out. The boat must not be allowed t o r i d e c l o s e t o t h e r e e f . This sounds easy, but
can i n f a c t be very d i f f i c u l t t o do without damaging t h e boat o r i n j u r i n g someone.
I t i s important t o r e a l i z e t h a t any approach t o a r e e f must be made with t h e boat normal ( p e r p e n d i c u l a r ) t o t h e r e e f margin, a s t h e b o a t can only be c o n t r o l l e d by movement ahead o r a s t e r n . A good p r a c t i c e i n any t r i c k y s i t u a t i o n i s t o drop an anchor some way out
from t h e r e e f , then a s t h e approach i s made, t h e anchor l i n e i s payed out u n t i l t h e b o a t i s n e x t t o t h e r e e f . The f i r s t person out w i l l hold t h e b o a t , t h e anchor l i n e w i l l keep t h e b o a t i n p o s i t i o n . The l i n e can be made f a s t and a n o t h e r l i n e o r anchor put on t h e r e e f , t h e r e b y hold- i n g t h e boat between t h e two l i n e s . This method o f coming i n on a l i n e has many a p p l i c a t i o n s ; a good example i s beaching a b o a t through a s u r f . Here, t h e l a s t s t a g e s o f t h e approach might b e t t e r be made s t e r n f i r s t , a s a wave b r e a k i n g over t h e bow i s l e s s l i k e l y t o f i l l t h e boat than one b r e a k i n g over t h e s t e r n . The above presupposes a l i g h t t o moderate s u r f . I n a heavy s u r f no a t t e m p t should b e made t o approach e i t h e r a r e e f o r an i s l a n d .
A windward approach can o n l y b e attempted d u r i n g v e r y calm weather.
Again t h i s i s o f t e n b e s t done by running back from an anchor l i n e , w i t h t h e utmost c a r e t a k e n t o i n s u r e t h a t t h e waves do n o t throw t h e b o a t onto t h e r e e f . The anchors a r e used t o h o l d t h e b o a t a t j u s t t h e r i g h t d i s t a n c e out.
The u t i l i z a t i o n of some n a t u r a l f e a t u r e s o f a r e e f can o f t e n make l a n d i n g much e a s i e r . For example i f t h e r e e f margin i s i r r e g u l a r , one o f t e n f i n d s r e l a t i v e l y calm a r e a s j u s t behind a s m a l l "headland" o r p r o j e c t i o n of t h e r e e f . A w e l l developed "groove and b u t t r e s s system"
can provide convenient l i t t l e "harbors" from which one can s a f e l y land, even i n f a i r l y rough s e a s .
WIND AND CURRENT EFFECTS
The e f f e c t o f t h e wind on t h e water i s t h e most important f a c t o r i n f l u e n c i n g t h e u s e of s m a l l b o a t s i n working around r e e f s . I n
r e l a t i v e l y shallow water a r e a s l i k e t h e Great B a r r i e r Reef a v e r y s m a l l i n c r e a s e i n t h e v e l o c i t y of t h e wind can, i n a v e r y s h o r t time, g e n e r a t e a v e r y rough s e a w i t h s h o r t , s t e e p waves. I n such a s e a t r a v e l i n g between r e e f s o r working t h e more exposed p a r t s o f r e e f s i s o f t e n unpleasant and can b e dangerous. The e f f e c t o f t h e t i d a l stream h a s a l r e a d y been mentioned. Experience with an a r e a w i l l enable a person t o judge what c o n d i t i o n s o f wind and s e a a r e most conducive t o s a f e and reasonably comfortable working, although t h e p a t t e r n i s o f t e n complex and n o t r e a d i l y understood.
Usually I seldom t r a v e l between r e e f s i f t h e wind i s blowing h a r d e r than 15 k n o t s , e s p e c i a l l y i f I must d r i v e i n t o t h e s e a s .
Running with t h e wind can be done a t wind speeds of 20 k n o t s o r h i g h e r . Only v e r y calm days a r e used t o v i s i t and work t h e v e r y windward a r e a s o f most r e e f s . Any s c i e n t i f i c p r o j e c t t h a t w i l l e n t a i l t r a v e l i n g over a mile o r working t h e margins of a r e e f should have a program t h a t i s
f l e x i b l e enough t o accommodate changes i n t h e weather. Given moderate weather conditions, f o r any wind o r t i d e , t h e r e is usually
-
some p a r t ofa large r e e f t h a t can be v i s i t e d . The l e e of any r e e f i s by f a r t h e s a f e s t place t o work, t h e flanks a r e often characterized by rough water and t h e windward areas, except i n a very calm sea, a r e dangerous.
When handling t h e l i g h t e r , outboard-powered boats i n a wind, it must be remembered t h a t they w i l l tend t o d r i f t sideways very quickly.
Any t r i c k y maneuvering should be done d i r e c t l y facing the wind. The wind w i l l a l s o tend t o blow t h e bow of t h e boat off-course s i n c e t h e bow
i s usually higher, and i s l e s s weighty. One has b e t t e r control of a boat i f i t i s run slowly up i n t o t h e wind o r c u r r e n t , r a t h e r than slowly
along with i t . This i s important when picking up a person o r a mooring f l o a t . When t r a v e l i n g any distance with an outboard boat it i s b e s t t o go with t h e wind o r waves. Excessive speed i n rough seas i s not recommended, as with a l i g h t planing boat i t i s possible t o plane down a wave and bury t h e bows i n a trough, o r t o be thrown sideways and l o s e control of t h e boat with p o s s i b l e d i s a s t r o u s r e s u l t s . I t i s s a f e r t o maintain a t l e a s t a reasonable speed, as t h e boat i s l e s s l i k e l y t o be
f i l l e d by a c r e s t i n g sea when t h e speed of t h e waves and t h e boat closely approximate each other. Heading i n t o t h e seas o r "punching i n t o it" can be a wet and thoroughly unpleasant business unless a t very slow speeds, y e t it i s perhaps s a f e r i n r e a l l y rough weather. I t i s important when c a l c u l a t i n g f u e l needed f o r a t r i p t o remember t h a t d i f f e r e n t sea conditions w i l l r e q u i r e varying amounts.
Be cautious when working i n an a r e a where a change of wind d i r e c t i o n can have serious consequences--in t h e t r o p i c s s q u a l l s can b r i n g on very sudden changes i n wind d i r e c t i o n and v e l o c i t y .
JUDGING THE DEPTH OF WATER
The color of open water on a c l e a r day with a high sun and a breeze w i l l i n d i c a t e t h e approximate depth very well a t close distances. Deep blue water i s about 50 f e e t o r more, l i g h t green o r blue-green water from several f e e t t o about 30 f e e t over a sandy bottom. Most important of a l l i s brown, which i n d i c a t e s r e e f below t h e surface of t h e water
(several inches t o 20 f e e t ) .
Judging t h e depth of water over t h e r e e f f l a t i s d i f f i c u l t because of varying c l a r i t y , wind e f f e c t s , e t c . Often only a few inches w i l l determine whether o r not one can use an outboard, t h e r e f o r e they a r e c r i t i c a l . The presence of niggerheads and o t h e r s c a t t e r e d d e b r i s
complicates t h e p i c t u r e . The b e s t method by f a r i s t o have a marker on t h e r e e f . A l i t t l e f o r e s i g h t here w i l l save many broken drive pins and damaged p r o p e l l e r blades. When water depth i s a t a l l questionable, never r e l y on your eyesight t o determine i t . Sometimes, e s p e c i a l l y with high cloud, polaroid sunglasses enable one t o pick out t h e margins of a reef more e a s i l y than with t h e naked eye.
NAVIGATION AND BEARINGS
This i s not t h e place t o explain t h e p r i n c i p l e s of navigation; one must assume t h a t any s c i e n t i s t t r a v e l i n g by open boat out of s i g h t of
land i s able t o read a c h a r t and p l o t a course. However a few notes might prove helpful. When determining one's p o s i t i o n on a r e e f , i t has been my experience t h a t it i s b e s t not t o r e l y too much on bearings
taken with a hand compass. The motion of a small boat i s u s u a l l y s o g r e a t t h a t bearings can only be considered approximate. Horizontal angles taken with a s e x t a n t a r e b e s t when p l o t t i n g one's p o s i t i o n from a small boat. I t is now p o s s i b l e t o buy small inexpensive, p l a s t i c s e x t a n t s which w i l l stand up t o such rugged conditions and y e t a r e s u f f i c i e n t l y accurate f o r most work.
Navigating between r e e f s with cays on them need not be s o p r e c i s e i f t h e distances a r e not g r e a t , a s islands can u s u a l l y be seen from 2 t o 8 miles away. However i t i s not wise t o r e l y on eyeball navigation as t h e v i s i b i l i t y a t sea i s a very uncertain t h i n g indeed. Always carry a compass. The choice of compass depends on many f a c t o r s : whether it w i l l be permanently attached t o t h e boat, i t s p o s i t i o n i n t h e boat, t h e
location of t h e motor, e t c . When s t e e r i n g from t h e s t e r n and using a small portable compass, I have found a small box compass made by t h e Swedish "Silva" company t o be very s a t i s f a c t o r y . This compass uses two p a r a l l e l l i n e s t o enable one t o s t e e r a p r e s e t course and has t h e
advantage of allowing one t o s i t a t some distance from t h e compass and s t i l l s t e e r a course. Other types require one t o be able t o read t h e a c t u a l degree markings which n e c e s s i t a t e s a f a i r l y l a r g e compass close t o one's face (awkward requirements f o r some small b o a t s ) . I might add here t h a t s t e e r i n g a compass course from a small boat t r a v e l i n g a t any speed is a t b e s t a r a t h e r uncertain business. I s h a l l not t r e a t t h e problem of compass deviation here, except t o say t h a t I have experienced
l i t t l e with aluminum boats and t h e compass a t l e a s t 6 f e e t from t h e motor.
I t i s u s e f u l when working a given a r e a t o c u t o r t r a c e out t h e appropriate section of a c h a r t including a compass rose, and t o lacquer o r varnish it t o a board. With a s e t of p a r a l l e l r u l e s , t h i s w i l l be most convenient f o r p l o t t i n g one's p o s i t i o n .
ANCHORS AND MOORINGS
A l l boats should have a t l e a s t one anchor aboard a t a l l times, plus s u f f i c i e n t l i n e o r chain t o be able t o anchor i n most depths o f water l i k e l y t o be encountered. On r e e f s located i n shallow s h e l f areas i t i s possible t o carry enough l i n e t o anchor p r a c t i c a l l y anywhere, and i n t h e advent of motor f a i l u r e , anchoring and waiting f o r help can save time and trouble, perhaps even l i v e s . With t h e development of various s y n t h e t i c ropes, e s p e c i a l l y nylon, very strong l i n e comes i n small diameters, and i t i s now p o s s i b l e t o carry enough l i n e t o anchor i n a t
l e a s t 30 fathoms of water. A tangled and s n a r l e d heap of l i n e i n t h e bottom of t h e boat i s worse than useless, and t h e only method t o c a r r y
a long l i n e i n a small boat i s on some kind of spool, which should have a hole through t h e c e n t e r so t h e l i n e can run f r e e , with t h e spool spinning on a b a r . The anchor should be attached d i r e c t l y t o a length of chain, then t o t h e l i n e . The longer t h e chain t h e b e t t e r , but because of i t s weight, 30 o r 40 f e e t a r e often a l l t h a t one can take.
The weight of t h e chain helps t o keep t h e p u l l on t h e anchor h o r i z o n t a l , avoids sudden jerks and it cannot be cut by rubbing over sharp
obstructions on t h e bottom.
The two most common types of anchors, and i n my opinion t h e b e s t , a r e t h e standard "pick" anchor f o r c o r a l o r rock, and t h e "Danforth"
f o r sand o r mud. The choice depends on t h e conditions anticipated;
often one i s j u s t i f i e d i n carrying both. Note: t h e Danforth anchor w i l l hold i n coral, but t h e pick anchor is almost u s e l e s s i n sand. However t h e Danforth anchor i s l i a b l e t o get s o well "hooked" i n c o r a l t h a t it i s very d i f f i c u l t t o e x t r i c a t e without diving. For small boats (12 t o 16 f e e t ) it i s o f t e n a good idea t o have an anchor s l i g h t l y l a r g e r than i s recommended f o r t h e s i z e of boat, as t h e Danforth anchor should be f a i r l y heavy i n order t o work e f f i c i e n t l y .
When anchoring, t h e b e s t procedure i s t o come slowly up wind o r current u n t i l t h e desired spot i s reached and then t o reverse and l e t the anchor go as t h e boat backs away. The amount of l i n e l e t out should be approximately 3 times t h e depth of water, more may be necessary i n sand t o insure a good hold. To bring up t h e anchor t h e b e s t method often i s t o have one person run t h e boat ahead while t h e o t h e r brings i n t h e slack l i n e u n t i l i t i s v e r t i c a l , then a good tug from above o r even s l i g h t l y ahead w i l l usually f r e e t h e anchor. I f t h e anchor has become fouled, one should t r y p u l l i n g from d i f f e r e n t d i r e c t i o n s , using a s e r i e s of sharp t u g s . Anchor with care, e s p e c i a l l y a t t h e end of t h e day. Many boats a r e l o s t every year due t o f a u l t y , inadequate o r even nonexistent ground t a c k l e .
When anchoring next t o a r e e f during low t i d e make s u r e t h e boat i s f a r enough out so i t doesn't swing i n a g a i n s t t h e r e e f with a change of wind. Two anchors a r e often required t o hold a boat properly. Near t h e r e e f c r e s t during high t i d e , note t h a t waves may begin t o break as t h e t i d e ebbs and water l e v e l f a l l s .
A mooring i s nothing more than a length o f chain o r l i n e , secured t o a heavy object t h a t cannot be moved by a boat p u l l i n g against i t . I t i s very u s e f u l when one works i n one a r e a f o r an extended period of time, and can be made by wrapping a l i n e around a boulder. A f l o a t w i l l help see and pick up t h e end of t h e l i n e . Some advantages of a mooring a r e : t h e l i n e i s much s h o r t e r than an anchor l i n e and therefore t h e swing of t h e boat w i l l be much l e s s , reducing t h e possib- i l i t y t h a t change of wind w i l l cause it t o be stranded o r damaged with t h e f a l l i n g t i d e . A mooring can be made more secure than anchoring a s t h e s h o r t e r chain can be much heavier and can be attached t o a heavy cement block.
I t i s worthwile, e s p e c i a l l y i n remote areas, t o give some thought t o t h e securing of one's boat f o r t h e night o r with t h e approach of bad weather. The l o s s o f t h e boat during a sudden storm o r change of wind a t night could be embarrassing, e s p e c i a l l y as i t i s simple and inexpen- s i v e t o secure i t properly.
SAFETY MEASURES
Before going anywhere i n a boat someone on shore should be informed of t h e d e s t i n a t i o n and estimated time of return; t h i s i s very important.
A l l boats should have aboard a t a l l times t h e following
items:
anchorp l u s s u f f i c i e n t l i n e , i f boat i s small enough a p a i r of oars, day and n i g h t d i s t r e s s f l a r e s , a l a r g e b a i l i n g bucket, s u f f i c i e n t l i f e preser- v e r s f o r a l l persons aboard, a small compass, a container of drinking water. I f a motor i s used, some t o o l s and spare p a r t s should be i n t h e boat; i f t h e motor i s an outboard carrying e x t r a shear o r d r i v e pins, a s e t of spark plugs and even another p r o p e l l e r i s a good idea. The above may seem l i k e a l o t of " s t u f f t ' but i n terms of human l i f e o r even inconvenience it i s not excessive.
I f possible boats should have b u i l t - i n buoyancy, which can be i n t h e form of foam p l a s t i c blocks fastened underneath t h e s e a t s .
I t i s a good idea t o time one's r e t u r n well before sunset, s o t h a t i f necessary a search can be made before it gets dark. Perhaps t h e b e s t s a f e t y device i s one of t h e small t r a n s i s t o r i z e d "walky-talky" r a d i o s . They a r e rugged and t h e more powerful ones have a range of up t o 20 miles i n a d i r e c t l i n e over t h e water. This w i l l enable one t o remain i n
contact with t h e base, and have much more freedom i n changing plans, without being forced t o r i g i d l y conform t o a prearranged schedule.
Now, a f i n a l word concerning s a f e t y while i n t h e water. When diving from a boat i n an a r e a s u b j e c t t o a t i d a l stream i t i s most important t o dive up-stream from t h e p r e v a i l i n g current, then i n ' t h e case of exhaustion o r a cramp a person can d r i f t back t o t h e boat. A l i n e t r a i l i n g i n t h e water behind t h e boat i s a l s o a good idea. Because of f r i c t i o n t h e t i d a l stream is not as strong on t h e bottom, and t h e r e - f o r e can increase almost unnoticed by a busy diver, who upon surfacing can f i n d himself being swept away with an empty a i r tank.
