outboard height on my 18

Beaver · #1 02-08-2013, 02:37 PM

Sorry if this has been covered a million times. I tried using search funtion and couldn't find anything.

I have an 18 CC with a 90 hp Tohatsu (3 cylinder so its pretty light). I think the motor may be too low since the cavitation plate is about 1" lower than the keel. My thought was to raise it at least an inch but maybe two. It seemed like I read where one guy had his set 1 1/2" above and liked it. Any ideas as to what it a good height for the 18? Thanks.

hugo · #2 02-08-2013, 03:06 PM

on any boat without a braket it needs to at least (the cav plate) level with the bottom of the boat. some like it higher. but never lower than that.

McGillicuddy · #3 02-08-2013, 03:45 PM

Yes, your motor is too low. Hopefully you have at least 3 holes to raise it. 1-1/2" is perfect on my 20' w/ a 300 lb Merc 115.

Highly recommend a 15p Black Max/Black Diamond alum prop, or a PowerTech MQF3, also 15p, if you go stainless. Great lift and maximum all around performance for said power and boat.

Beaver · #4 02-08-2013, 04:36 PM

Excellent. I have three holes left on the engine. Thanks for the feedback.

McGillicuddy · #5 02-08-2013, 11:50 PM

If your Tohatsu has the 2.33 gear ratio, you may be able to swing more prop. What year is your motor and what prop are you using currently?

Good luck. and keep us posted on your change in performance.

Beaver · #6 02-19-2013, 07:21 PM

Sorry for the late reply. The motor is a 91 90A. WOT seems to be about 5400 and the motor seems to get it up on plane pretty quickly but I have noticed a little porpoising and splash back on the transom which got me thinking about the height. Im checking with buddies to see if anyone has a motor puller I can borrow. Ill let you know the results.

Beaver · #7 04-17-2013, 03:11 PM

Ok...so I raised the motor three holes and was able to ditch work a little on Monday to try it out. Water was flat in Mission Bay (San Diego) with just a little wind texture.

First impression was that I didnt like it. Prop began to cavitate almost immediately. Unless I had the trim all the way in before I took off it would cavitate. It didnt seem like I picked up any more top end or that it plained any quicker. My concern was that in snotty ocean conditions it may cavitate a lot. The cavitation plate was above the water line when running and seemed to be fanning water behind the motor (i.e. sheeting off to both sides).

To me it seemed like there were more negatives than positives so I'm going to drop it back down 2 holes and see how that works.

Fr. Frank · #8 04-17-2013, 09:02 PM

Drop it one at a time.