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Post by davidbennett on Mar 29, 2017 16:29:18 GMT -1
great cheers!
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Post by davidbennett on Mar 30, 2017 17:02:13 GMT -1
couple of observations today: noticed the cavitation plate is about 2 inches under the bottom of the transom back board - I think these need to line up don't they? also after looking at some footage of the back of the boat on full throttle - you can see water getting thrown up into the air just above the prop and if I remember some water was spilling in over the transom - maybe some hydrofoil stabilizer fins would stop this and maybe get rid of the cavitation/ventilation - what do you think?
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Post by philpot on Mar 31, 2017 6:52:46 GMT -1
I have reservations as to how effective hydro fins are. They will help bring the boat on the plane but they are a pig for transporting the engine in the car because the fins lift the prop when the engine is laid down so you then have to raise the top of the engine so no oil starts to run back up from the prop to the engine. They may do what you want, I just don't know to be honest. It may be worth checking web info and any dealer who you know and trust rather than some dealer who is just happy to sell you gear.
2'' is not ideal but to raise the engine 2'' is going to need some strong fabrication to the transom. If you test the boat with about an inch of packing under the engine clamps to see if that has the desired effect. The out should be okay as is but because of the issues you have, try the test.
Don't forget to check the floor pressures though, very important.
Phil
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Post by davidbennett on Mar 31, 2017 6:59:39 GMT -1
ok cool I ll check the pressure next time I inflate cheers dave
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Post by davidbennett on Mar 31, 2017 7:13:46 GMT -1
presume this how it should look? Dave
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Post by davidbennett on Mar 31, 2017 7:25:59 GMT -1
oyeah mines a 2 stroke so I shouldnt have the oil issue should I? Dave
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Post by philpot on Mar 31, 2017 13:56:06 GMT -1
I checked my engine position David and it sits with the cav plate 2.5'' below the transom bottom but mine is a RIB with fibre glass floor and you will find the response to cavitation / ventilation varies from boat to boat. We are back to that trial and error method I think. I will be worth the effort because in one session, you will be able, with any luck, to see the effect of raising the engine. It is always better if you can do the tests on flat water if at all possible because you will be testing with good water flow under the boat. When in rough water, there is always a chance of disturbance from wave motion so not so easy to make a judgement.
On a 2 stroke it should be okay but many years ago when I had one fitted to an old Selva, I was warned that it was better to sit the engine at the same angle that it would be if there were no fins fitted. As the engineer supplied me with the engine and others, I had no reason to doubt him so I always did this by packing the engine head. Not sure what the fins are like now but the ones I had did flex a little when lain on their side. I have not used fins for at least 20+ years so they may be better nowadays.
Phil
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Post by davidbennett on Apr 3, 2017 11:31:37 GMT -1
i wont be able to test on water for a couple of weeks but I inflated it and put the engine on mines actually 4 inches from the bottom of the transom to the top of the cavitation plate - this could be the problem? Attachments:
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Post by davidbennett on Apr 3, 2017 11:33:22 GMT -1
also I noticed the was on a slight angle due to the setting of the trim I ve moved it from position A to B as well so it sits more at a 90 degree angle Attachments:
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Post by davidbennett on Apr 3, 2017 11:33:57 GMT -1
it should read.. the motor
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Post by davidbennett on Apr 3, 2017 11:37:38 GMT -1
mine probably looks similar to this cavitation plate inline with the front of the inflatable keel Attachments:
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Post by philpot on Apr 3, 2017 16:10:42 GMT -1
Right David, lets just take the engine mount first. Get the outfit on the water and take a good look at the angle of the engine shaft compared to the water. We are looking for 90 degrees. If it needs altering, do so and that is my start point. It is not possible to gauge on dry land just how the engine sits so it must be done on water. Now the fun begins because you need to check this whilst on the plane and don't try it in a narrow river as I did on one occasion, nearly finished up the bank. Take a friend with you so that he can look at angle of the engine shaft or you look while he takes the tiller. It is likely that it will have changed because of the power working against a flexible hull will force the shaft to 'dig in' and therefore you will need to move the location pin until you are happy but only move the pin, one hole at a time. Again because of the power thrust from the engine, it is really important to have all the tubes and floor at the correct pressures in order to offer as rigid a structure as possible.
Cavitation plate height at 4'' does sound to be too deep so the tests we spoke about earlier with pieces of wood under the engine clamp to raise the height I think will be needed.
It must be remembered that we are talking about a boat that flexes all over the place so to completely remove issues like yours may be impossible as water conditions change as does the hull shape. What we want to do is try to eliminate as much as we can and the things we have already gone through will help but the transom depth has been made to suit a standard shaft engine so it shouldn't need a large lift for the engine but you can never be sure.
What make of boat, size and model is it because I don't think you have actually said unless my aging memory has forgotten.
Phil
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