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I have extended the transom on my 57 Sea Coaster to accomodate a new Mercury 50 hp ong shaft. For practical reasons regarding installation the boat guy made the transom almost 22". I am experiencing some steering control problems.

20" is the accepted height and the cavitation plate should be even with the boat bottom or slightly below. At 22" this is not the case. The cavitation plate is 1 1/2" above the bottom of the boat. The bow hooks to the left at about 22 mph. I have a lot of wasted horsepower.

Are these handling problems due to the transom being too long and the prop not far enough in the water?

Tom

Tom,
The transom is defenetly too high for one thing. Cut it down so the anti-cavitaion plate is at or below the bottom of the hull. With the plate higher the trim tab/ anode is not doing anything for you at all.
Once that is done then see if you still have a problem with steering control. If so you then need to look at the bottom of the hull. It may have a haug in it which is causing the problem along with the transom being to high.
Basiclly start with the one change then see if you need to go farther.

Good Luck!

Phill

Yup, I agree. The transom is too tall.

Andreas

When I did the transom over on my 62 Sea Lancer I was puzzled by the fact that all the information on boat motors new and old called for a 20.5" transom height and the height of my original Lancer transom was 22.25". My keel strip was also short by approximatly 18" on the rear of the hull and I mistakenly assumed that it had broken off and was not restored to proper length by the previous restoration. I installed the new keel all the way to the transom and then discovered that was not correct. As I was well along with a finished hull and I liked the idea for complete clamping of the garplanks I elected to leave the keel at its full length. I was having some shrink cracking problems that needed to be addressed on the new transom and had not completed the final cut on the installed transom. I decided to lower the transom height by 1+1/2" from the original 22.25" putting my transom height at 20.75" with the keel all the way back to the edge of the transom. I am happy with my decision as it placed the bottom end of the motor in what appears to be perfect alignment with the bottom of the hull. The keel's protrusion into the slipstream under the hull has no impact on any performance that I can tell. I would be interested why, and for what purpose, Thompson went with the shorter keel and excessive transom height if anyone knows. Just passing on what worked for me. Rod

I just measured the transom on the 1961 Thompson Bros. (Peshtigo) Sea Lancer model 950 I am restoring. She measures 21 1/4 inches. I am sure it is original. Also, the outer keel stops 30 inches from the end of the transom, again original factory installation.

I also just measured the '57 Peshtigo Sea Lancer (my user boat) and the transom is exactly 21 inches. The outer keel on this boat extends right to the transom, but it's only about 1/2 inch deep at that point.

I am certain I made a new outer keel for the '59 (Peshtigo) Sea Lancer I restored last year. I cannot recall where it ended, but think I ended it short of the transom.

On the '65 Peshtigo Sea Lancer I restored two years ago, I made a new outer keel and extended it all the way to the transom, tapering her down in depth to about 1/2 inch at the end. This boat was missing the outer keel when I got her, so I don't know what the original looked like. I cannot recall the height of the transom, but a previous owner had cut out a notch where the motor mounted. I installed the '67 Merc 110 HP outboard at that height and the boat spit water all of the place and was squirrly. I then took the motor off and blocked up to the original height. That solved the problem. Ultimately I sold the boat without a motor.

Andreas