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Old 31 March 2009, 05:42   #31
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Country: UK - England
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Originally Posted by willfinch36 View Post
I've sort of got a problem like this - prop is fine though, probably because I have hydrofoils on? when you get up to top speed and trim the engine up, if you steer hard left then right and then left again the boat will feel very unstable as if it could easily flip, dont really want to take the foils off though as there will be a few holes in the engine where they were... but might try it...
You always not steer hard left then hard right. Most boats when trimmed out will feel heavier than normal when turning.
If you trim it in a bit for turning it'll turn alot quicker and sharper.
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Old 31 March 2009, 08:05   #32
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Originally Posted by mike-m View Post
Neil,

Sounds to me like you are driving the boat with too much "nose down" trim. This will give an unpleasant feeling of the boat trying to "twist" to port and it will also be in grave danger of bow steering (bow digs in and boat pivots violently around it).

Try trimming the nose down but NOT fully (those hydrofoils will magnify the effects of trimmer movement quite a bit), then steadily open the throttle. As the boat goes "over the hump" and the bow drops, you will hear the engine rpm increasing without further throttle movement. At this point you should be trimming out/nose up and you will find the boat will behave more normally. Once you have established a comortable trim position, try trimming in and out and notice what happens to your bow spray - the more you trim in/down, the further forward you will see it coming from under your boat, the further out/up the further back it goes. If you trim out/up too much at speed, the boat will start to "chine walk" - possibly quite aggresively, given that is a lot of horsepower for the size of boat.

I think the suggestion to remove the fins is probably a good one, at least until you have become comfortable with the trim effects of your new engine. Engine offset doesn't sound like the root cause here, so leave it alone until everything else is checked?

The cavitation plate should be level with the bottom of your transom in an ideal world, but half an inch lower will not adversely affect you and may improve your "grip" in turns.

That prop is shot - get a decent stainless one and enjoy yourself!!

This is all IMVHO, so if I am teaching you (or anyone else) to suck eggs, please excuse me....

Regds

Mike
Mike, I think you are right, I was coming to that conclusion while I was on the water, plus having read up on hydrofoils they apparentkly "lift" the stern.

My usual set off routine is to be fully trimmed in, to give max manoevrability coming from shallow water and to then set off get on the plane and then trim out to reach cruising speed etc.

The port list was always at the start, I was hitting the trim button immediately to lift the engine, and throttling back. From standstill setting off again, this seemed to remove it, although not completely, i.e 90 degrees to a small swell re created it again.

I think some experiments with trim and a trim bar, (is that what its called), to prevent the engine going too low, may well fix this.
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Old 31 March 2009, 10:24   #33
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Yep, I had identical problem with the old Yam on mine. Had trim tabs (one bent!) when I got it, removed them, which improved it a bit, and then played with the trim bar. Unfortunately the "shortbread block" saga then reared it's ugly head so I never got to a final conclusion, but trimming out did seem to improve matters at speed. The engine was mounted dead centre.

Maybe it's a Humber design feature!
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Old 31 March 2009, 18:49   #34
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sorry if this is hijacking the thread a wee bit, but...

I'm about to have a new motor fitted and have been reading with interest about the location of the cavitation plate, whether 1" 2" 3" above the bottom or whatever folk have experimented with.

Sorry if this is an obvious question, but how do you play around with that? Does that mean drilling new holes in the transom or is there another adjustment somewhere? If it's new holes, I'd have thought putting a selection of holes so close together would be bad news?
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Old 31 March 2009, 19:00   #35
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Originally Posted by DonMacN View Post
sorry if this is hijacking the thread a wee bit, but...

I'm about to have a new motor fitted and have been reading with interest about the location of the cavitation plate, whether 1" 2" 3" above the bottom or whatever folk have experimented with.

Sorry if this is an obvious question, but how do you play around with that? Does that mean drilling new holes in the transom or is there another adjustment somewhere? If it's new holes, I'd have thought putting a selection of holes so close together would be bad news?
The mount bracket will have a few mounting holes to set it at different heights.
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Old 31 March 2009, 19:03   #36
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Ah! OK, thanks. The old engine's gone, so I'd nothing to go out an look at. I'd hoped it would be something like that.
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