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Old 30 January 2014, 04:58   #1
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hysucat hydrofoil

Not the most clear footage but just a bit of a glimpse of the Hydrofoil in action.

I had to wedge myself between the hulls to get this footage.
Luckily the conditions were fairly calm.
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Old 30 January 2014, 05:45   #2
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Ive got an 8.5m, with a couple of Suzuki 175's on the back.

Ive not had much experience with it yet and would be very interested in any advice you have for trimming yours.

When using mine recently I had it running at about 47 knots, by trimming up/down it made a difference of 3-4 knots.

But at slower speeds it seemed to behave differently. I need to play about a bit more, it seemed at some speeds I trimmed out, others I trimmed in.

How do you trim it when its not on the plane ?

So before I spend a day messing about Id like to have a start point to begin experimenting from. Any suggestions / experiences would be welcome.

Cheers.
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Old 30 January 2014, 07:24   #3
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I personally trim right in / down when at displacement speeds unless I am in very shallow water when I will trim up sufficiently to ensure the prop does not get dinged.
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Old 30 January 2014, 07:33   #4
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Mmmm, I need to do some experimenting then and see how it affects my boat.

Without trying it, I would have thought you would not tirm up or down at displacement speeds. That would leave the prop to push the boat along - flat, rather than slightly up or slightly down.

How do you trim your boat if you want it to come up onto the plane then ? Trim it out - to lift the bow ?

With the little/limited experience I have had it does seem my boat comes up on the plane in a different manner to a normal V shaped hull. I reckon some runs with a note pad and co-driver are in order.

Any excuse for messing about in boats
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Old 30 January 2014, 08:45   #5
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Hi A,

After going out in your boat I spent a bit of time on the internet to try and find out a bit more about the handling and trimming. From what I found out it doesn't need to be trimmed out to the same extent as a deep V because the hydrofoils need to be fairly flat/level to work properly so trimming the bow up like I have to and most deep Vs do may not work. Your boat seemed to just rise up onto the plane fairly flat, rather than climb over a bow wave. In fact when we first set off your trims were about 1/3rd trimmed out and the boat popped quite happily onto the plane no drama or climbing onto the plane. (Mind you twin 175s does help!)
So the usual practice of trimming in to keep the bow down when going onto the plane would probably still apply, there would also be a need to trim out a bit (so the props are not trying to lift the back of the boat and are just pushing the boat forward) perhaps to level trim or maybe a bit more once at cruising speed and above. But trimming out a lot might be counter productive as the bow doesn't really lift and if it does, is not that efficient for your hull.
It sounds like you are going about it the right way, trying things out and making a note of what is happening, speed and fuel consumption etc. Generally its a balance between speed, fuel efficiency and ride comfort. All boats are different and yours is more different than most!

Enjoy the testing. If you need a co-pilot (I have a note pad) you know how to contact me!
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Old 30 January 2014, 09:10   #6
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Cheers, I may well give you a shout sometime

Im anxious to learn as much as possible and take advantage of others experience.

This weekend Im planning on messing about on the Thames - so not much chance of trimming at speed. But next time Im down on the south coast I may well post up a thread and see whos about for some testing / learning.

Thanks.
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Old 30 January 2014, 14:02   #7
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I'll try a simple explanation of trim:

You want the engine leg vertical in the water at displacement speeds so that the prop is pushing water horizontally out the back. On most boats trimmed fully in gets the leg vertical in the water but some boats mat need to be trimmed out slightly to achieve this.

Once up on the plane the boat is generally sitting at a different angle, usually with the bow slightly higher, so you trim out to get the engine leg vertical again. If you trim out to far you will hear the prop ventilating (sounds like it's a car wheelspinning as the prop is too near the surface and is sucking in air and the prop blades have lost grip with the water) and you just trim in a bit to correct. Trimming out to the optimum point will give you more speed for a given throttle setting and lower fuel consumption. Always trim back in for tight turns, and trim back out again once you are going straight.

In heavy weather you can use trim to keep the bow up in a following sea, or keep the bow down when ploughing into a head sea.

Chris
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Old 30 January 2014, 14:18   #8
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When driving my SR 5.4 in speed restricted ares( 5+- knots), strange enough, it seams like trimming plenty out drag caused by the transom is less.

So get same speed with less rpm and less consumption when engine is trimmed out, this compared to when propeller axle is in horizontal position. Possible due to less turbulence in the water around the propeller trimmed out?
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