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Old 21 July 2016, 13:26   #1
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Hydrofoil fitted

I've just fitted a hydrofoil to my 15HP mariner on a Quicksilver 3.4 SIB.
It seems to get up on plane sooner but speed hasn't changed noticeably !
The reason for fitting it in the first place was some times the boat feels really responsive and other times feels sluggish. Is that sea conditions ? Flat calm or decent swell.
We are just messing about a few hundred yards out but the boat feels totally different from one day to the next ??
Any ideas
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Old 21 July 2016, 13:32   #2
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Thats prety much what a foil will do sometimes they even slow the top speed due to extra drag but they usually help plane more level and at slower speed
Your problem sounds possibly pressure related due to differing temperature first thing I'd check was the inflation pressure then try again
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Old 21 July 2016, 14:38   #3
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Top speed isn't my top requirement, staying on plane at lower speeds is. My StingRay hydrofoil meets that requirement. Planes at a lower speed sooner is real easy with my 20 HP Suzuki.
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Old 21 July 2016, 15:17   #4
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Pressure is spot on to the book after returning to shore.
Feels much more responsive on mirror flat compared to a bit of swell.
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Old 21 July 2016, 16:21   #5
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Quote:
Originally Posted by Boatinggary89 View Post
The reason for fitting it in the first place was some times the boat feels really responsive and other times feels sluggish. Is that sea conditions ? Flat calm or decent swell.

Any ideas
Hi Boatinggary.. when you mention it feels sluggish ..do you mean the OB doesnt seem to rev so fast as well as the boats performance feeling sluggish ?

I ask as i know my OB on the F Rib planes no problem in normal condition..but when it gets rough and I have extra weigh of water in the bottom of the boat.. because my power to weight ratio is not so good..the OB will start to struggle..and because it cant plane ..it cant reach its normal max revs of around 5k..it stays at around 3k until it builds up the speed to plane again ..which can take a good time. It therefore feels very sluggish at times in marginal conditions

A 15 HP on a 3.4 should be fine but if heavy loaded ..it could make it marginal ? Listen to the revs on the OB when it gets sluggish..if it sound lower in revs..it could be weight issues ? Especially if you needed the fins to help it plane to begin with.

Just a thought
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Old 21 July 2016, 16:32   #6
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If it's handling that feels sluggish, it's probably due to the inconsistent wetted areas of the hull. My 14' Achilles would get pretty flighty in short chop.

jky
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Old 21 July 2016, 16:33   #7
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>>> problem sounds possibly pressure related due to differing temperature first thing I'd check was the inflation pressure then try again

If this Quicksilver is an air floor that is quite possible... they can be very pressure/load/sea state sensitive.
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Old 21 July 2016, 16:56   #8
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All of the above but get a Tinytach on there to see what's really happening with the engine.
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Old 23 July 2016, 12:31   #9
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Thanks for the replies. I'll try the tachometer when I can get one. It is an air floor quicksilver but all pressures are correct according to my BT12 digital pump.
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