Transom Bracket - twin outboards

[McGillicuddy]

I think John is dead on about the negative trim - you have excess and that need a way to govern that, wedges or a 2x4 - whatever keeps your prop shaft and cavitation plate mostly parallel to your keel. Like Dana Carvey mimicking Uncle George Sr., "Don't want to be \ nor / wanna be somewhere in between, sure..."

Fr. Frank's suggestion on measuring engine height is very important. Straight edge on bottom of hull in line with each motor skeg and cavitation plate parallel to hull bottom. Seacrafts run best with cav plate about an 1-1/2" above the hull bottom, additionally, Armstrong asks for 1" of rise for every foot of bracket setback...you do the math.

Finally, I'm with reelescape - ditch the foils. Use the the trim tabs for efficient planing and hull control.

Different props may help but I think the other three issues should be dialed in first. Good luck, and keep us posted.

[Fr. Frank]

Gillie said:

Seacrafts run best with cav plate about an 1-1/2" above the hull bottom, additionally, Armstrong asks for 1" of rise for every foot of bracket setback...you do the math.

Finally, I'm with reelescape - ditch the foils. Use the the trim tabs for efficient planing and hull control.

Different props may help but I think the other three issues should be dialed in first. Good luck, and keep us posted.

That 1.5" inches where Seacrafts do so well is for transom mounted motors. For every foot of bracket, add 1 inch to the 1.5" above the hull starting point. So for a 30" setback bracket, your starting point would be having the bottom of the cavitation plate 3.5" above the hull.

[JohnB]

What I found is boats with flatter deadrises are closer to 2" per foot of setback, and boats with deeper deadrises are closer to 3", but it really comes down to having someone driving, and someone looking at the cavitation plate when your running.

I moved my motor up and down 4 times before I finally was statisfied. As stated above, get the straight edge, and I would start with the cavitation plate 3.5" above the straightedge. With twin 4 strokes on the back, it is problably going to ride a little lower in the stern.

Then dial in the negative trim with the engine trim.

[lobo1]

open to all suggestions but the motors actually got a little better with the addition of the foils. however, they are easy to put on and take off; these newer ones do not require drilling holes in your motor - just have to loosen one bolt and they are gone.
the motors are supposed to go up two holes today and hopefully I can get it out to see what that does tomorrow.
will post when I have something new.

I REALLY do appreciate all the ideas!

[doodlebug]

when you move thim put thim all the way up, I dont think with where your bracket is mounted you can get thim high enough and keep the hydrofoils for my 150's with thim
on I can cruse at 3100 when rough without 4100 is the slowest they are made to run on top or above water
not below

[Bushwacker]

What I found is boats with flatter deadrises are closer to 2" per foot of setback, and boats with deeper deadrises are closer to 3", but it really comes down to having someone driving, and someone looking at the cavitation plate when your running. . .

I think you're right, John. Mine is at 3.5" with 30" setback.


It handles great but could probably go a little higher because cavitation plate is still slightly under water at typical cruise conditions. Motor is already at max height however, so I'd have to redrill the mount holes to go higher. Don't know how much higher I could drill the holes on this bracket.

[doodlebug]

mine is set at 5 inches now the 250's were set at 7
bigger gearcase also required scoops for cooling

[McGillicuddy]

With the nearly 1000 lbs of motors hanging 2+ feet back you may very well need the SE foils. They certainly have benefits. I meant to edit that... Good luck, it looks like you're on your way.

[Fr. Frank]

Denny, your 3.5 inches of height at 30 inches of setback fits the profile of having 1 to 1.5 inches above the keel when mounted at the transom, plus 1 inch additional height for each 1 foot of setback. (30 inch bracket = 2.5 feet of setback) And that's just the starting point for adjusting the motor height.

[lobo1]

what are you guys running for props? seems to be predominantly 4 blade props. The guy from the Yamaha parts (Andy) on The Hull Truth - told me that the prop I am running - the Yamaha "Reliance" 19 has a history of poor performance on many different applications.