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Old 23 May 2023, 19:37   #1
Country: UK - England
Join Date: May 2023
Posts: 1
Help with outboard set-up on transom

First, I'd like to say how grateful I feel to have found this forum! I am dealing with this from a position of ignorance; I've never had to adjust much of anything on any watercraft I've operated. So now that I have to, I'm totally clueless! I am hopeful some of the experts here can guide me to where I need to be since the local "experts" seem to know as little as I.

DETAILS: My boat is a Scout 365. It's similar to a Ka-Boat I'd say. The transom height from factory is 12". My Suzuki DF2.5hp has a transom top-to-cavitation plate distance of 17.5" despite being a short shaft. So that would put the cavitation plate 5.5" below the water, which is too deep per the outboard owners manual which calls for 0-1" below.

WHAT I DID: I asked for some advice from various locations and how to get a more appropriate depth. It would seem I'd need to make a riser. Which I did. A small issue with asking the local "experts" was whether the cavitation plate measurement should be from 0-1" below the TRANSOM or below the PONTOONS, which are the absolute bottom of the boat. Opinion was 50/50! So I went with BOTTOM OF PONTOON.

RESULTS: The transom turned out well and looks OEM. See images. This puts the outboard cavitation plate .25-.375" below the pontoons. For further troubleshooting reference, this puts the same plate approximately 2" below the transom. So not a great deal of difference between bottom of transom and absolute bottom of boat/pontoons.

At up to 1/3 throttle, boat runs 8km/h. Beyond and at full change. Bow rides high. Boat not planing. Not a sharp, beautiful wake behind boat.

Now I understand this boat/motor combo isn't meant for speed. But similar boats with same power reach nearly 15km/h when they are planed out.

My question is...what now? I'm clueless how to proceed to "fix" this. Lower engine? Raise engine? Hydrofoil installed on cavitation plate? Go on a diet? LOL I'm 185lbs and realize having more weight forward is helpful.

Any ideas?? Also not sure if this post is more appropriate in General or Motor forum.

Thanks so much for any insight!! Click image for larger version

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RRocket is offline   Reply With Quote
Old 25 May 2023, 10:48   #2
Country: UK - England
Town: Leicester
Length: 5m +
Engine: 135hp Mercury
Join Date: Sep 2013
Posts: 1,365
Too much weight aft? If you look at their own video it shows the driver well forward & using a long tiller extension. on the 'Product' page.

Outboard trimmed too far out?

Outboard too small? Again, for your boat their site shows maximum size of 3.5hp and recommended size 3.5hp.

paintman is offline   Reply With Quote
Old 28 May 2023, 19:27   #3
Country: UK - England
Town: Leicester
Make: Yam
Length: 3m +
Join Date: May 2019
Posts: 249
2.5hp is very small. I've not heard of much planing with that kind of motor. Do you have examples of that boat planing with that size motor?

All of the messing baout with transom height etc will only become beneficial if improving the planing behaviour. At displacement speeds it won't make much odds and I'm not convinced that engine can get you on the plane, especially if you weigh 185lbs.

You could try a tiller extension and get well forward. Before Wasing any more money you could try a diy one with a bit of old waste pipe.
Blankton is offline   Reply With Quote


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