Motor positioning

[bigoldboy1]

I have only recently bought my boat for skiing and have noticed the outboard is mounted almost 3inches off centre and the cavitation plate is about an inch higher than the very bottom of the hull. Would these things make much difference and is it worth sorting them out.

 

[Kenny Bush]

Re: Motor positioning

Bigoldboy, That motor should be centered on the keel. The cavatation plate sounds like it is perfect.......it should allways be an inch or two above the keel. That motor off center sounds scary.........Does it turn to one side strangely? I know my big boat with twin outboards torques up on one side when I run 1 engine. Goodluck...BushCat

 

[bigoldboy1]

Re: Motor positioning

Thanks a lot Bushcat.

 

[bigoldboy1]

Re: Motor positioning

Thanks a lot bushcat. I,ll move the motor into the centre and leave the hieght as you suggest.<br />Cheers Bigoldboy1

 

[bowhuntrrl]

Re: Motor positioning

I've always been told that the cavitation plate should be exactly even with the bottom of the hull. Why would you set it higher ????<br /><br />bowhuntr

 

[ob]

Re: Motor positioning

bowhuntr,For optimal engine performance it is practice to mount engine as high as possble on transom without experiencing cavitation or prop slippage while on a plane and executing sharp port and starboard turns.This will allow your engine to run with the least amount of prop blade drag and exhaust back pressure.In some cases it will give your engine a bit more WOT rpm capability.

 

[KIWI MERCMAN]

Re: Motor positioning

bigoldboy1<br />Does your boat have a running pad?, and what size hp do you have on it?<br />The reason I ask is that some boats with pads do have the engine off set to the port side a little as this overcomes prop torque on light weight high hp boats. It stops it from laying in on one side. <br /><br />Kiwi

 

[bigoldboy1]

Re: Motor positioning

Thanks everyone for your opinions but now I,m really confused. Does the engine need to be central on the transom and should the cavitation plate be level with the bottom of the hull or not? The boat is a 14 foot Marina and the engine is a Johnson seahorse 75 apparently from 1981 and it came with doelfins already bolted to the cavitation plate. Now I still need help please. Sorry Kiwi I don,t know what a running pad is.

 

[ob]

Re: Motor positioning

First thing I would do is perform a water test on the rig with the current set-up and see if there are any major handling issues.It is likely to have a steering glitch with a 75 hp mounted as you state ,up to three inches off center.If it is rectified ,it will entail drilling four new holes and the ones omitted will need to be dowel plugged and sealed to prevent any water intrussion into transom.The optimal height of the anti ventilation plate in relation to the bottom of the boat varies from rig to rig and will have to be determined from a water test.With boat on plane at near 3/4 throttle ,execute sharp port and starboard turns and note if there is any prop slippage or cavitation as a rapid increase in rpms would indicate.

 

[Hooty]

Re: Motor positioning

Run the boat as is. If you don't have any steering or cavitation problems, leave it like it is.<br /><br />c/6<br /><br />Hooty

 

[steelespike]

Re: Motor positioning

A 14 foot with a 75 that sounds like it could<br />be over its rated capacity.

 

[bigoldboy1]

Re: Motor positioning

Thanks Spike. what does this mean as in being over rated. will the boat not perform correctly or is it because the motor is to heavy and the boat will be to low in the water?

 

[Jack Shellac]

Re: Motor positioning

I don't believe I'd rush to change anything before testing it out on the water. Like Kiwi, I've seen motors deliberately mounted a little off center. Usually it's big motors on relatively light boats to help offset prop torque. A 75 HP on a 14' boat may fit this description depending on the boat construction. I go with the "test it before you change it" ideas. Even if the 75 is overpowering the boat, you don't have to run it wide open if you're not comfortable with it.