20 inch transom versus a 25 inch transom

N

nastyquedawg

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I am restoring a 1974 21ft Beechcraft center console boat. The boat was originally designed with a 20 inch transom. I plan on putting in a 25 inch transom but wanted to know if the boat was designed for a 20 inch motor will making a taller transom to use a 25 inch motor have a negative impact on the boats performance.
 
Bondo

Bondo

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Re: 20 inch transom versus a 25 inch transom

nastyquedawg said:
I am restoring a 1974 21ft Beechcraft center console boat. The boat was originally designed with a 20 inch transom. I plan on putting in a 25 inch transom but wanted to know if the boat was designed for a 20 inch motor will making a taller transom to use a 25 inch motor have a negative impact on the boats performance.
Click to expand...

Ayuh,... It'll raise the center of gravity...
 
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Georgesalmon

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Re: 20 inch transom versus a 25 inch transom

It will change the CG slightly but should not hurt anything else as far as performance. After all, the prop will be in the same place in relation to the bottom. A higher transom will be safer in following seas too.
 
jbcurt00

jbcurt00

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Re: 20 inch transom versus a 25 inch transom

A longer shaft motor will also impart more torque at the transom clamp, it'll have a 5" longer lever between the prop & the motor mounts.

So you'll want to make sure you make a new continuous transom assembly, not just fab a 5" addition & attach it to the existing transom...

Why do you want to go up to a 25" motor? Do you already own it, and there's not a motor already on the boat, or it's non-running?
 
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nastyquedawg

Petty Officer 3rd Class
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Dec 25, 2008
Messages
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Re: 20 inch transom versus a 25 inch transom

I have a 25 inch motor that is a 1985 Yamaha that was on the boat before I began restoring it. The previous owner had an aluminum plate made so the boat could receive a25 inch motor. When I removed the plate, I discovered that the original transom height was designed for a 20 inch motor. The motor that I have on my 17ft center console is giving me problems. It has a 20 inch transom. I was contemplating buying a new 20 inch 150 hp motor and use it on my 17 ft boat until I finish restoring the 21 ft boat and reduce the current replacement transom to a 20 inch instead of a 25 inch.
 
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