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Old 03 December 2008, 05:11   #11
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I would trim the leg in as suggested above to avoid slip and then I would experiment with lifting the engine up a couple of inches on the transom as this will give you back some speed.

Ultimately if you don't have power trim then its all about finding a balance between speed and grip.

Chris
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Old 03 December 2008, 05:30   #12
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However I do have an stainless prop at home, but this is a totaly different size, this is 10" x 10". The prop on the pic is an original yamaha prop in aluminium size 9 7/8" x 12".
Still not sure what each of the numbers exactly stand for, then the bigger the number the bigger the size.
Maybe somebody can also help me with that?
the two numbers are (1) the pitch of the prop (2) the diameter of the prop. So I think you have a 10" diam x 10" pitch S/S prop and a 9(7/8)" diam x 12" pitch Aluminium prop. Going down in pitch (12-10") will lose you some top end speed. Going up in diameter 1/8" will probably not be obvious, but will be slightly harder to "turn" as will, the heavier s/steel so you might lose some revs. On the other hand your acceleration will improve.
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Old 03 December 2008, 05:30   #13
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Chris - wont raising the engine put the prop closer to the surface of the water ( as it runs off the hull at planning speed ) and risk pulling in more air ? I'm no expert on this as I've only had it happen a couple of times & its solved on my boat by trimming right in in the turns.

As you say will trimming in give the biggest improvement then upping the motor will give back the performance ?
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Old 03 December 2008, 05:37   #14
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However, does anyone know why this happens and what I can do about it?
I'm sorry to say that you may not be able to do much about the problem with that hull. It's only medium-V and the tubes are mounted quite low. As a result, when you do a tight turn, the tube will be foced into the water on the inside of the turn, and the keel will lift out of the water. Sorry but I think you don't have the right sort of hull for what you want.
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Old 03 December 2008, 05:50   #15
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By the looks of what most of you are saying, it looks like a combination of factors.
The medium V hull is definately the case, however, when in plane it lifts quite a bit out of the water. But for sure not as much as bigger RIB's with much deeper V.

I've no powertrim so no way of trimming down when going into turns.
So will bring down the engine 1 hole, and see what this will do for turning, top end speed and overall handling.

The prop is not the best but good enough for the engine / boat combination I think. So for the little extra gain by going for a better prop, is not worth the money. Better save that for my next engine 60 hp or so....

Think I've summed it up correct like this.
Thanks everyone for your input!

If anyone has some other vision, please let me know!

Vincent
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Old 04 December 2008, 02:51   #16
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I'm sorry to say that you may not be able to do much about the problem with that hull. It's only medium-V and the tubes are mounted quite low. As a result, when you do a tight turn, the tube will be foced into the water on the inside of the turn, and the keel will lift out of the water.
I think there is something in that too ,.. not so much the hull v depth,.. but the tube size in relation to the hull and stern weight, they look large and will provide a lot of lift in a turn , with an engine that doesnt weigh very much in relation to them. Your engine is well deep enough as it is IMO
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Old 04 December 2008, 05:16   #17
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Think there is a good point in that.
And the boat is slightly underpowered, aiming for 60hp next year or so. Depending on depth of wallet......
Hope with a heavier and more powerfull engine, the balance will be better and especially the lift during planing.

ps. Bigmuz, don't want to be a know it all, cause I sure am not, but with Honda's VTEC is spelled VTEC and not VTECH. Couldn't help myself seeing this in your personal info on the left of each post.
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Old 04 December 2008, 11:03   #18
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You could contact the rib manufacturer and ask him what is the factory deep V bottom/anticav plate height parameters best peformer recommended, maybe he has the light at the end of the tunnel.

Happy Ribbing
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Old 04 December 2008, 13:32   #19
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Chris - wont raising the engine put the prop closer to the surface of the water ( as it runs off the hull at planning speed ) and risk pulling in more air ? I'm no expert on this as I've only had it happen a couple of times & its solved on my boat by trimming right in in the turns.

As you say will trimming in give the biggest improvement then upping the motor will give back the performance ?
When I read the post that Vintec placed saying....

"The anti vent plate is on the front of the shaft about 2 cm (little less then 1 inch) below the transom, with the current trim possition the end of the anti vent plate would be a little bit above the transom"

The fact the vent plate is 1" below the transom at the front and above the transom at the back suggested to me that the engine is trimmed quite far out which would certainly explain the cavitation. So by trimming in this will resolve the cavitation but at the expense of a fair bit of speed. I would be looking to then lift the engine until the cav plate was level or slightly above the bottom of the transom in order to recover that speed and fuel efficiency.
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Old 04 December 2008, 13:58   #20
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There's just one slight issue in raising my engine. The engine is attached to the transom by the turnable screws at the front end of the bracket (don't know how to call these....), so no bolts are used.
I didn't use bolts yet because I didn't want make holes in the transom, since the transom is lowered for my shorthaft engine and I'll have it brought up to normal hight when I'll get a bigger engine.

So how can bring the engine up without drilling holes in the transom?
Or is it no problem to drill holes and later close them up again?
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