Transom and motor mount position.

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Jeffmaturo

Jeffmaturo

Well-Known Member
Joined
Jan 20, 2015
Messages
547
[SIZE=11pt]When designers and builders like Kris, Shawn, Mike Carl, etc. design their individual tunnel hulls how exactly do they determine where the transom goes? Specifically where should the pivot point be for the OB? [/SIZE]

[SIZE=11pt]Do tunnels run better if the transom and mount are closer to the bow or do they run better closer to the stern? How exactly do you figure out how far in or out that you want your motor mount to be? [/SIZE]

[SIZE=11pt]Was wondering how both affect performance? [/SIZE]
 
After placing the transom in various locations ranging from flush with the back of the sponson running surface to inserted up to 2 1/2" on a 7.5 tunnel, I now position the transom so the center line of the pivot pin is even with the back of the sponson running surface. I think Rod Geraghty said that was good location. Anyway, it seems to work fine for my current WOF designs.

JD
 
I was also wondering about motor mounts themselves. Some are made to work very close almost flush with the transom and then there are others that extend over an inch behind it.
 
Jerry Dunlap said:
After placing the transom in various locations ranging from flush with the back of the sponson running surface to inserted up to 2 1/2" on a 7.5 tunnel, I now position the transom so the center line of the pivot pin is even with the back of the sponson running surface. I think Rod Geraghty said that was good location. Anyway, it seems to work fine for my current WOF designs.

JD
Click to expand...
X2...this is very important Jerry and spot on. It's not about the transom, it's all about the pivot pin placement.
 
Barring all other design aspects.. pin position is understeer.. and oversteer.

I like the pin at or near the back of the sponsons. BUT.. the sponson design itself is way more critical regarding a neutral boat.

Having the pin at neutral just removes one of the comparative variables during the design phase.

Grim
 
Last edited by a moderator:
Which pin position creates understeer, is it with the pin in front of the back of the sponson ?
 
This is more of a self-test let's see how right/wrong I am. Relative to rear of the sponsons, placing pivot pin significantly forward creates under steer while placing significantly behind creates over steer. Coming from a washed-up-haz-been.

Wallster
 
still holding my breath for you Wallster the hazzbeen
default_wink.png


get that Dragon out of its cage some time an come out an PLAY

marty

how RIGHT OR WRONG
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is he
 
I put it at 20mm inset on my M11 because Mike had his Villain at .75"
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On my M18 I put it at what ever it is because it looked good
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There is a point that too far back it loads the prop too much, drastically creating the issue when you go to set into the corner. That's where Carl figures in both variables:

Swivel pin centerline from transom.

Prop hub face from rear of sponson.
 

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