Originally Posted by Richard Selman
Installed my 280 kg F250 Yamaha with a starboard offset of 1.5" as per osprey's guidlines. With just me in the boat (starboard seat), side to side trim was OK - may be a slight lean to port. When my mate of similar weight sat in the port seat, the lean to port at speed was more noticable. I have now installed the FT9.9 auxillary (45kg) on the port side (where there is more room of course) and now the lean to port is worse. The closest I can put the engines together is 20.5" centre to centre
Calculating moments 280 kg offset by 1.5" is 105 Nm. 45 kg offset by 19" is -108 Nm. I have therefore totally reversed the effect of offsetting the main engine!
The options I see are:
1. Shift the whole lot to startboard. I think I can move the main engine by 2" easily. This would give me a net moment of 31 Nm. Less than I originally had with the main engine alone but better than what I have. This is the easiest mod to make and leaves me with the most room for trim tabs. Only four holes to fill. Is 3.5" too much engine offset?
2. Swap the aux over to the other side. This would give me 351 Nm or more than three time what I had with the main engine alone.
3. Centre the main engine and swap the aux over to the starboard side. This would give me 230 Nm or about twice what I had before the auxilliary.
Going to do some test work with weights as soon as I can but I was interested in whether anyone else had ever tried to calculate what righting moment might be required.
Last two mods would make the auxilliary clash with the dump trunk and I would probably need to shift it to the port side. Bit reluctant to drill more holes. Always thought that the dump trunks were a pretty simple but basic solution to the problem. I would have thought a big bore valve mounted on the inside of the transom would be better - anyone tried anything line this?
I am in the throws of the same question. My offset is almost 2 inches on an 8.5 Hull, but because my helm is to port, dual batteries and AUX motor head is on port also, I still get a cant to port when under way at speed. I can trim this off but the hull position is not correct and fails to use the bows' ability to slice water at this trim, so the aux is getting reversed, and the motor has been moved a further inch to starboard, but I havent tested the new config as yet.
Interstingly, I tried a 4 blade prop as advised by Barrus, but its had no effect, other than give better grip in corners etc, and paddle wheel effect has not been reduced, despite their advice it would be.. although in some installations I dont doubt it would.. but it didnt in mine. I'm intersted to read your calculations
See if I can find a photo