Transom Height: 15 or 20-inch - Moderated Discussion Areas

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Author Topic:   Transom Height: 15 or 20-inch

alberg35 posted 04-29-2006 10:10 AM ET (US)
I'm restoring my "new" 1967 13-foot Boston Whaler boat. I'll soon be looking for a new or used motor to re-power and need to decide whether to leave the present 15-inch transom as it is, or go ahead and raise it to 20-inch. Aside from convenience, is there any inherent advantage to a 20-inch transom over a 15-inch in terms of performance, safety or seaworthiness? I'd appreciate any comments. Thanks
jimh posted 04-29-2006 10:27 AM ET (US)
A 20-inch transom height has an advantage over a 15-inch transom height because it has higher freeboard at the transom. This should create less chance for water to come aboard. This probably increases the seaworthiness and safety of the boat. I do not believe it has an effect on performance, at least not in terms of providing greater speed.
On the other hand, if you had a 15-inch transom and a 15-inch shaft motor, the engine weight would be carried five inches lower, and this would tend to lower the center of gravity of the boat. This might improve the roll characteristics of the hull.
If you choose to made a modification to the hull to raise the transom height to 20-inches, you must perform the modification in a suitable manner. If the modification is not done well it will detract from the value of the hull.
Tom W Clark posted 04-29-2006 11:16 AM ET (US)
No practical difference in performance but the higher transom will increase the chance that the lower unit of the motor clears the surface of the water when tilted.
AZdave posted 05-01-2006 01:03 AM ET (US)
You will also have a larger selection of possible motors if you build up the transom. Fifteen inch, electric start, remote steering outboards were getting a bit scarce when I did this a few years ago. Boat wakes (from other boats) seem to come closest to sweeping in over the lower transom. I can't say that I've ever really had a problem with this, but the extra freeboard might be nice. On the other hand, if you recover swimmers, skiers and tubers over the stern, they might appreciate a lower transom. Dave

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Author	Topic: Transom Height: 15 or 20-inch
alberg35	posted 04-29-2006 10:10 AM ET (US) I'm restoring my "new" 1967 13-foot Boston Whaler boat. I'll soon be looking for a new or used motor to re-power and need to decide whether to leave the present 15-inch transom as it is, or go ahead and raise it to 20-inch. Aside from convenience, is there any inherent advantage to a 20-inch transom over a 15-inch in terms of performance, safety or seaworthiness? I'd appreciate any comments. Thanks
jimh	posted 04-29-2006 10:27 AM ET (US) A 20-inch transom height has an advantage over a 15-inch transom height because it has higher freeboard at the transom. This should create less chance for water to come aboard. This probably increases the seaworthiness and safety of the boat. I do not believe it has an effect on performance, at least not in terms of providing greater speed. On the other hand, if you had a 15-inch transom and a 15-inch shaft motor, the engine weight would be carried five inches lower, and this would tend to lower the center of gravity of the boat. This might improve the roll characteristics of the hull. If you choose to made a modification to the hull to raise the transom height to 20-inches, you must perform the modification in a suitable manner. If the modification is not done well it will detract from the value of the hull.
Tom W Clark	posted 04-29-2006 11:16 AM ET (US) No practical difference in performance but the higher transom will increase the chance that the lower unit of the motor clears the surface of the water when tilted.
AZdave	posted 05-01-2006 01:03 AM ET (US) You will also have a larger selection of possible motors if you build up the transom. Fifteen inch, electric start, remote steering outboards were getting a bit scarce when I did this a few years ago. Boat wakes (from other boats) seem to come closest to sweeping in over the lower transom. I can't say that I've ever really had a problem with this, but the extra freeboard might be nice. On the other hand, if you recover swimmers, skiers and tubers over the stern, they might appreciate a lower transom. Dave