Motor height - Merc 150 seapro

[salmonkiller01]

My Hourston 20 on a stepped bracker and a 275 Verado was like your boat. Too much weight in the stern. It should have been 3” above the bottom of the hull. It ran best at 5”. However as it was a bracket it had room for the water lift. On yours raising it too much will get to a point of cavitation.
Are you batteries in the transom? If so how many and can you move them? Yes a pain. My Hourston batteries were under the driver seat to move weight.
When I dropped to the 200 merc it was 3” above bottom of hull. I also save over 100 pounds.

If you have to or can move your batteries is blue seas posts to save rerigging all the way to your engine.

 

[EstevanPoint]

I think you are close on mounting height, one hole should do it. Your photo showed that the anti-cav plate was visible, but not skimming the water. Its close - just no quite there. Each hole gives you a 3/4" rise. Rough rule of thumb is that if you take a straight-edge along the bottom of the hull and extend it back to the anti-cav plate, the underside of the plate should be 1" higher for every 12" from the transom - but that's just a rough guide - mine was higher than that - very much depends on hull shape.

There are a lot of terrible youtube videos on this, but here is the best one I found. It starts off with the motor mounted too low, and then he raises the motor and tests a few different props. It shows you what you should be looking for in terms of how the anti-cavitation plate should be skimming the surface. The visuals are a useful reference.

As a side note - the anti-cavitation plate should be skimming once you are at regular cruising speed - you don't need to test it flat out. The full throttle test is to get the prop pitch correct.

Sorry for the derail…

Any advice for twins? I’ve been considering raising my motors but can’t find a straight answer with twins. I have a deep V, 24 degree deadrise. A straight edge runs from the hull the middle of the motor shaft basically right on plane with the cab plate. So that means half is covered half is exposed. Any wisdom to share on that front? I feel like I need to raise them.

 

[zurk]

the official yammy manual says ...

https://yamahaoutboards.com/getattachment/b24d5f4c-4839-4484-895b-2cfaf85837ff/BoatersLogVol4No6Portablesimage4.jpg

with twins take a ruler between both on the plate and use that to intersect with the bottom of the boat corresponding to each lower edge of the twin. since your water flow is at your deadrise angle you will have to measure from the lowest edge of each twin plate to the lowest edge of the hull in front of each twin plate.

 

[Aquaholic]

the official yammy manual says ...

https://yamahaoutboards.com/getattachment/b24d5f4c-4839-4484-895b-2cfaf85837ff/BoatersLogVol4No6Portablesimage4.jpg

View attachment 125678

Maybe for a work boat or a boom boat. Your sailing brain is going in the wrong diection.

 

[SpringVelocity]

I found this diagram a while ago when I was doing my pod project.

 

[zurk]

Maybe for a work boat or a boom boat. Your sailing brain is going in the wrong diection.

if youre saying yamaha is wrong thats fine. it works ok for my non sail boat so YMMV.

i'll trust the manufacturers recommendations thanks.

 

[Pineapple Express]

the official yammy manual says ...

https://yamahaoutboards.com/getattachment/b24d5f4c-4839-4484-895b-2cfaf85837ff/BoatersLogVol4No6Portablesimage4.jpg

This is completely not applicable to @Macdeep or anybody else who has chimed in on this thread.

 

[SpringVelocity]

Do you know if the boat builder had two different locations for the fuel tank depending on if the boat was built to be an outboard or stern drive? Some other builders do it.

I think the 182 might have the tank a little further back vs 185.

 

[SpringVelocity]

This is completely not applicable to @Macdeep or anybody else who has chimed in on this thread.

My thoughts as well...

 

[Aquaholic]

I think the 182 might have the tank a little further back vs 185.

Which model was factory outboard?

 

[salmonkiller01]

Sorry for the derail…

Any advice for twins? I’ve been considering raising my motors but can’t find a straight answer with twins. I have a deep V, 24 degree deadrise. A straight edge runs from the hull the middle of the motor shaft basically right on plane with the cab plate. So that means half is covered half is exposed. Any wisdom to share on that front? I feel like I need to raise them.

Best way to check is have your boat at cruising speed and look at your cavitation plates. Are they buried or can you see them. Too high with twins and one motor can cavitation on hard turns at speed

 

[SpringVelocity]

Which model was factory outboard?

182

 

[brutus]

Waited a bit on this one,mine is on a bracket also, Sherwood set it 3” above, on plane was a spray fest, raise it up 2 holes so about 5 “ now, still a bit low IMO, barely any spray, if I raise it up more it will cavitate in choppy conditions, so like all have said its trial and error, also went with a Suzuky swinging a way bigger prop then my Honda, did purpose a bit, so move stuff around towards the bow in the cuddly and now happy with it. Also don’t have to pay a dealer to move it up or down I have the techno at my shop to do it myself. Also have one of those Bob hydrolic jack plate in my shop still in the box, haven’t bothered with it because I am fine the way it rides

 

[salmonkiller01]

Waited a bit on this one,mine is on a bracket also, Sherwood set it 3” above, on plane was a spray fest, raise it up 2 holes so about 5 “ now, still a bit low IMO, barely any spray, if I raise it up more it will cavitate in choppy conditions, so like all have said its trial and error, also went with a Suzuky swinging a way bigger prop then my Honda, did purpose a bit, so move stuff around towards the bow in the cuddly and now happy with it. Also don’t have to pay a dealer to move it up or down I have the techno at my shop to do it myself. Also have one of those Bob hydrolic jack plate in my shop still in the box, haven’t bothered with it because I am fine the way it rides

Stepped bracket or follows hull?

 

[brutus]

Stepped bracket or follows hull?

Stepped

 

[brutus]

This is it

 

[CatchAll]

Anyone who has experimented with their motor height knows that the straight edge off the keel technique is just a rule of thumb for finding the starting point. After that you can only find the best motor height for your application through trial and error. The guys who set it and forget it either get lucky or don't seem to mind excessive spray, porpoising, or poor fuel economy. Even the manuals acknowledge that there is a range of heights. The diagram above says 0" to 1", so what is right? When I got my old campion 185 the motor was buried all the way. It road terrible, burned too much fuel, porpoised at anything over half throttle, and made a huge wake coming off plane that would damn near swamp the boat (slight exaggeration, but it was weird). The mid-90's campion 185s with the stepped transom require the motor to ride high and it took me a long time to figure it out. I went up every hole one step at a time. Each time it got better; less spray, better fuel economy, quicker on plane, less porpoise. After the motor was as high as it could go I added a manual jack plate so that I could get a little higher and fine tune the motor height by turning a few wrenches. Eventually you find the spot where the motor ventilates going over waves or turning hard. At that point you go back down a hole or two. After that you play with props. Adjusting the motor height will change the wide open throttle RPM because there will be less drag with less leg in the water. After the motor height is set right you might be able to add an inch or two of pitch. The boat I got after the campion 185 had motor mounted all the way down too. I jumped it up three holes after the first ride and the difference was night and day.

The manufacturers can't give a recommendation that works perfectly for every hull. They all ride differently and the water flowing off the bottom of the hull will rise at a different rate depending on a variety of factors. Deadrise seems to be a big factor. I'm not an expert, but I experiment with stuff and this is what I have observed.