Engine Mounting Height

[Tin Cup]

How does one confirm the correct mounting height of the outboard? I suspect that that my outboard is not mounted at the proper height, i.e prop depth in the water. My basis for this is the significant amount of spray that goes straight up and into the motor mount bracket area. I don't see this spray pattern on any of the other outboards on the water, I took pictures but they did not come out very well.

[21ftcc]

http://www.marinepartsman.com/installin ... -boat.html

This might help.

[aluminumdreamer]

Stupid question, but do have the engine trimmed too far down?

[welder]

When running on a plane your cav plate [ the large flat Horizontal part above the prop ] should be right on the water surface.

As said above , if you are to far trimmed down it will spray up and in a fan pattern .

The cave plate should be parallel to the water and flush with the very bottom of the hull .

If your on a Bracket , the cav plate should be 1" lower than the bottom of the hull for every foot behind the transom as a rule of thumb then tune from there.

[Tin Cup]

Thanks for the help. I did check the full range of trim, this does not correct the problem. After my initial post, I did some research on the web and found similar info as Welder reports. It looks like I'm 1-2 mounting holes too low.

[pjay9]

If your on a Bracket , the cav plate should be 1" lower than the bottom of the hull for every foot behind the transom as a rule of thumb then tune from there.

I thought if you were on a bracket it was to raise the engine as the clean water is coming up to meet the lower unit after leaving the transom...isn't that what jacking plates are about...since plates can be ordered in 4, 6 8 10 inches back of the transom...I thought it was a clean water thing. That is the way it worked on my old 1959 Larson with an after market tilt and trim which moved the engine back about 8 inches and the cav plate was one inch higher than the bottom of the boat and I gained 2 knots from that along with being able to trim it for speed and ride. Had that boat 23 years. I know it was a tupperware boat but an absolute unique runabout and always drew a conversation. Now the Riader draws attention. Capt PJ

[Chaps]

I've been having a good old time playing with engine height & trim using the Porta hydraulic motor bracket on my LaConner as it will raise or lower the engine 17" vertically. I've found that ideal motor height is a variable depending on sea conditions, how a boat is loaded, what your HP to weight ratio is, what type and pitch prop you have and what speed you want to run at. The motor height sweet spot varies quite a bit depending on those factors.

I usually start out with the engine kind of deep in the water when I first push the throttle forward as it tends to jump up on plane quicker. After I'm going and the throttle is set for the rpm I want to cruise at I push the bracket up button and raise the engine up high enough to where the prop just starts to lose its grip then I drop it down a little so it stays hooked up. Then I adjust my trim up to where the boat starts to porpoise just a little then trim it down a bit till that stops happening. Those settings change quite a bit depending on if things are choppy or calm and/or how many people and how much crap and fuel I've got on board.

So now I'm totally perplexed by Tin Cup's question because I've seen that ideal motor location can vary quite a bit and that hard & fast rules may not work in all cases or on all boats especially if you need to handle a variety of conditions. I'm not sayin' everyone should run out and get a bracket, just saying that the right answer probably won't pop out of a rigging manual.

[welder]

HOLY SMOKES, PJ , you are right , ONE INCH HIGHER is correct .

My bad , I went backwards .


And I get lost a lot , just ask Cgrand

[Tin Cup]

I finally got to use The Cup after lifting the engine two mounting holes about 3 weeks ago. As I hoped, this greatly reduced and almost eliminated the fan spray pattern from behind the boat when on plane. I expected slightly better performance, but not 20% more speed :shock: 20' pacific with 140hp Johnson (made by Zuke); before the lift, she maxed out about 33mph @ 6200rpm, now she runs 40mph. Also she is much quicker to get on plane and obviously more fuel efficient The engine is still a little too low, I'll now raise it to the last hole.