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PostPosted: Wed Mar 07, 2018 6:49 pm 
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Joined: Sat Apr 26, 2014 6:01 am
Posts: 179
Location: Orlando!
Not trying to set a speed record, it’s just what I have.

My intention is to build a mount out of 2x12 and 1/8x3/4 aluminum angle extrusion. The plank will be firmly attached to the top of the rear cross brace just inboard of the gunnels on both sides, and the 4pc of angle “iron” will have 2 of them mounted along the top of the gunnels in the storage area, and 2 from near the top of the plank at an angle to near the center of the pieces atop the gunnels. I think this design will distribute the torque and weight loads well. The motor is listed as 46 lb.

The only outboard that I’ve seen greater than 2.5 has been on a TI so I have a little trepidation going into this. What kind of forces will be generated against the hull by the motor and/ or water? Is it enough to cause short term failure or long term fatigue, or is it all within the stress tolerances of this craft?

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PostPosted: Thu Mar 08, 2018 9:27 am 
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Joined: Fri Aug 11, 2017 9:16 am
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Location: San Diego, CA
I have a Suzuki 2.5hp 4 stroke and an old Merc 4hp 2 stroke. The first test of my mount I ran the 2.5 all day. At the end of the day I swapped over to the 4hp for a test, broke the rudder pin within 5 minutes. This was on a TI.


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PostPosted: Thu Mar 08, 2018 11:19 am 
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Location: Colorado
broke the rudder pin.. the forces on the rudder go up with the square of boat speed (in theory) but the speed difference between 2.5 hp and 4 hp probably isnt that much and still likely not as high of speeds as you can get to under sail power. I would think a fair amount of the sailing we do in higher winds is probably harder on the rudder pin than even a 4hp outboard can dish out..

So.. the rudder pin breaking could be just a coincidence??? Just my .02.. could be wrong.


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PostPosted: Thu Mar 08, 2018 12:55 pm 
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I ran a Tohatsu 3.5HP four stroke for several months and had no issues with the TI. And I've heard of at least two people who run 5HP motors.

As long as you have a good feel for the boat and are aware of the forces being applied then you shouldn't see any major issues. Just don't push it beyond anything you think is reasonable. You always have control of the throttle and you can make the determination of how much power to use at any given time.

The only drawback I see is the extra weight.


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PostPosted: Thu Mar 08, 2018 3:01 pm 
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Joined: Sat Apr 26, 2014 6:01 am
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Location: Orlando!
Thanks for the replies so far. My trolling motor battery weighs about 15 pounds more than the outboard but it's not cantilevered over the side either.

I'm curious what the specific conditions were when the rudder pin broke? WOT? Turning a little too sharply?

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PostPosted: Thu Mar 08, 2018 3:26 pm 
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Joined: Thu Aug 16, 2007 2:25 pm
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Location: Central Coast NSW Australia
The rudder pin broke on my maiden voyage (Sep ‘16) with the Suzuki 2.5 motor. I’ve since put over 80 hours of motoring plus much more sailing and have not broken another pin, so it probably was coincidence.
I also thought the negative was the extra weight of the Honda 4hp/2stroke motor ...until I googled the specs, which were basically the same as the Suzuki 2.5/4 stroke.
I agree with Walt and Pro10is -the difference between a 2.5/4hp shouldn’t be a concern, especially if you avoid WOT.


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PostPosted: Thu Mar 08, 2018 9:26 pm 
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Joined: Sun Apr 20, 2008 6:18 am
Posts: 2983
Location: Sarasota,Key West FL
Yea the beauty of using bigger motors, ( or twin motors like I had) is you can get the boat up to reasonable speeds, (not crazy speeds) at much lower throttle settings, the benefit of that is the motors running at idle or just above idle get great fuel economy and are extremely quiet, ( similar noise output of a torqeedo, ( aka...PWM diode squeal)).
Try to keep the boat under 10mph, someday I’ll explain all that goes wrong when tryin to run these boats faster, (pretty much everything fails, lol).
FE


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