Yamaha 55BEHD prop

[Magnet6x6]

I've got two 55hp BEHP engines on the back of a 25ft dive boat.<br /><br />Its normal load is 6-8 adults 6-8 cylinders, 80lt of fuel and a heavy cool box.<br /><br />The boat doesn't seem to go as well as I would have expected. If there is a swell the boat struggles to climb and takes too long to get back to full operating speed. Similarly one engine won't put it on the plain full or empty.<br /><br />How do I calculate the correct props for the set up?

 

[rickdb1boat]

Re: Yamaha 55BEHD prop

2 55's may not be enough power for your rig. The best and only way to calculate the right prop size is to measure full throttle RPM's and see if they are within specs. Are the engines still running at peak performance or has this changed at all lately. Is the boat new to you? Has this always been a problem with this boat and motor set-up? 6-8 adults , 80lt of fuel and a heavy cool box. That's a lot of weight for those motors to pull. Ideally, one engine should be able to plane it out with a light load...What pitch props are you running now?

 

[Magnet6x6]

Re: Yamaha 55BEHD prop

Hi Rick,<br /><br />Thanks for the reply. The engines are running well and there's no noticeable detioration in performance.<br /><br />I know its a small set up but it should perform better than it it is. I'm currently running <br />11 3/8 X 12. I've borrowed some 13 to try but I think the pitch needs to go down rather than up.