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Old 06 June 2013, 15:05   #1
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SIB in heavy seas - ~4ft waves - how to navigate safely with speed ??

i have a 10.5ft soft inflatable with alum floor and 15HP. goes ~30kph with two on board + fuel + gear. caught in relatively bad seas (4ft waves). waves were 45-65 degree angles with 2-3 ft spacing in deep water (21 miles offshore by GPS). it planes well in 2 ft waves but with 4 ft it was hitting the water pretty hard so i went at 1/4 throttle and 8kph. took nearly 2 hours to return.
any idea on how i can go faster in heavy seas with a SIB ?? is there something i can add (maybe a foam block or inflatable triangular block at the back) to convert the planing hull shape of the SIB to a displacement hull so it rides faster in heavy seas ??
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Old 06 June 2013, 15:12   #2
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To go faster you have to add a couple of meters to your length! Or go downwind.

Displacement speed on a 10.5ft boat is about 4 knots. So about the same speed you were travelling.

Not sure where you were, but the whole excursion sounds incredibly iffy (and lucky). 21miles offshore in a 10.5ft SIB?!?
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Old 06 June 2013, 15:17   #3
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My SIB is 9ft. long. It's a category below yours and I take it all sorts of places and get raised eyebrows. However, I'm inclined to agree with most of what captnjack says. You need a bigger boat..., you're waaaay outside the envelope!

Simply put, a 4 foot wave (which is commonplace everywhere) has reduced you to crawling for two hours. In two hours, things can get a lot worse. There's a limit to what a 10ft SIB can handle.
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Old 06 June 2013, 15:41   #4
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i would agree a bigger boat is needed , having just done sibfest durdle door i can honestly say it was pretty mental on the way back i couldn`t see most of the way due to the splash mist from smacking the waves,it was a case of judging the waves inbetween the bounce so glad i was out with ribnet and in particular xs400
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Old 06 June 2013, 15:45   #5
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Quote:
Originally Posted by captnjack View Post
Not sure where you were, but the whole excursion sounds incredibly iffy (and lucky). 21miles offshore in a 10.5ft SIB?!?
I know I do my fair share of crazy stuff but I have to agree, that's a long way offshore in what is effectively only a rubber dinghy.
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Old 06 June 2013, 15:58   #6
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i have a 10.5ft soft inflatable with alum floor and 15HP. goes ~30kph with two on board + fuel + gear. caught in relatively bad seas (4ft waves). waves were 45-65 degree angles with 2-3 ft spacing in deep water (21 miles offshore by GPS). it planes well in 2 ft waves but with 4 ft it was hitting the water pretty hard so i went at 1/4 throttle and 8kph. took nearly 2 hours to return.
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Old 06 June 2013, 18:43   #7
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you're waaaay outside the envelope!
Very funny expression, almost flipped my desk chair laughing +1 on that.

Zurk, do like doing cracy things myself, but venturing on a 10 Ft sib that far from coast is out of this cracy world..

Happy Boating
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Old 06 June 2013, 19:01   #8
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Hmmmmm
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Old 06 June 2013, 20:59   #9
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i planed for a bit when coming back. then the sea got too rough so it took two hours to return after that. probably planed for 15 minutes at full throttle, then had to cut back which accounts for the time difference.
we go out further all the time (its 30 miles or so to nanaimo). i dont think its too dangerous as you cant get swept out into open ocean without hitting land unless youre really really unlucky. and plenty of boats are out here. we even one paddle boarders coming through but the coast guard stopped him doing the crossing as he was not wearing a life jacket.

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Old 06 June 2013, 23:44   #10
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I believe you are in a over your head running that far out in such a small craft. You don't need to worry about being swept to sea, as you are already there. Hope you are actually wearing your type 1 PFD while running. A type 2 would be nearly useless in seas bad enough to cause a capsize.

Having other boats in the area may not be so comfortable if you realize what would be involved in getting you aboard safely in rough water. This could put a rescuer in danger as well as you and your crew. His first responsibility is to get his own crew home safely, so you may remain in the drink much longer than you planned.

Once the seas become rough enough that you cannot make speed, you are in a bad situation which should be avoided if at all possible. You should carry enough fuel to be certain that your craft can slug it out at displacement speed for however long it takes to reach sheltered waters. The cost of fuel will be the last thing on your mind if the tanks run dry in sloppy water. A sea anchor might be a good investment for you.

In my humble opinion, you are putting others in harms way as well as yourself by running so far in such a small boat.
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