long shaft motor vs short shaft for 17 inch tansom

[mlarson29]

i have an old 1960 starcraft jet that ive been slowly fixing up for the last 5 years and its time for a new motor.
the motor i have right now is a 1970 evinrude 33hp ski twin. honestly when it works its a great motor, but several times a season its down for various repairs which isn't surprising for its age. i measured the leg on the evinrude and it appears to be around 18 inches.

the new motor i have purchased (2019 tohatsu 30hp)can either be bought with a 15" or a 20" shaft. they have stock of both so when i go to pick it up next week i can swap to a short shaft if needed. i am also worried about the extra weight bringing it down in the back but plan on moving the batteries forward to save some weight. the ski twin i have wieghs in at 140 pounds and the tohatsu that i bought weighs in at 173 pounds. would it be better to keep the 20 inch shaft and build up the transom a couple inches so it sits a bit higher in case the boat dips a bit or get the short shaft?

also i would like to rebuild the transom what is the best material to build the new transom out of. i am also planning on adding a aluminum plate in the back for extra strength.

 

[jbcurt00]

also i would like to rebuild the transom what is the best material to build the new transom out of. i am also planning on adding a aluminum plate in the back for extra strength.

Ask about rebuilding the transom in the Restoration forum.....

A solid rebuilt plywood transom doesnt require a metal plate.....

 

[jbcurt00]

Check to confirm the actual Short and long length of the Tohatsu, many arent exactly 15 or 20in, because boats arent all 15 or 20in transoms like your 17in
..

 

[gm280]

Interesting concept in this one. A too long shaft will work but increased foot drag will effect your speed and you will not be as able to get into shallower water as one that fits perfectly.

One the other size, the shorter shaft has to have enough water entering to keep the engine cool. It will work but engine cooling has to be looked at real carefully. If the water cooling is still workable, it will run very well.

A compromise could be the longer shaft motel and set it higher on the transom to accommodate the correct length. Just some issue to thing about.

 

[mlarson29]

Check to confirm the actual Short and long length of the Tohatsu, many arent exactly 15 or 20in, because boats arent all 15 or 20in transoms like your 17in
..

yah sounds like a plan. ill phone tohatsu tomorrow morning

 

[racerone]

Does the 33 HP motor have a 5 " spacer between the exhaust housing and the lower unit ??----If the answer is no then it is a short shaft.

 

[Sea Rider]

Big dilemma, been there myself. Had a boat with 17" transom height. A short shaft Tohatsu produced excessive over revving on other than non flat calm water cond, worse on tight close turns at speed. Installed a 20" long shaft and added a SS anti splash plate as seen on pic to flatten incoming water flow against the exiting flow. The back splashes were totally cancelled out...



For me it's much better than redoing raising the whole upper transom. If using a long shaft motor mounted on a 17" transom will produce excessive water splashes out or even over transom which will slow combo down at speed besides showering yourself it it's a tiller version...



Pics due to long and extreme water experimentation speaks for themselves..

Would like to hear what Tohatsu recommends in your particular case...

Happy Boating