Motor Length / Transom Length

schooner · #1 04-23-2007, 12:35 PM

Boat is a 1985 23 Sceptre. This is really pretty basic so I'll apologize in advance...I bought a new 225 Johnson / Suzuki last year and have been trying to get it dialed in right. Its a 25 inch shaft. The measurement from the lip of the transom where the engine mounts to the bottom of the Vee is 27 inches. The cavitation plate above the prop sits about 2 inches higher than the bottom of the vee. Should I have bought a 30 inch motor. The boat is a 1985. Was the 25 inch transom standard then? Were 30 inch motors even available then?
Thanks

Fr. Frank · #2 04-23-2007, 01:00 PM

You're good. Your cavitation plate width is about 5"-6", and the outside edge of the cavitation plate should be level or a half-inch above the bottom of the boat roughly 2 1/2" outside of the centerline, or in a vertical line from the edge of the cavitation plate. Give me a little bit and I'll make a very rough graphic of what I mean.

Fr. Frank · #3 04-23-2007, 01:31 PM

This is what I mean.

Fr. Frank · #4 04-23-2007, 01:35 PM

The measurement of shaft length to transom should be made at the outside edge of the cavitation plate. The proper view from the rear should be as depicted, NOT with the centerline of the cavitation plate even with the lowest point of the hull. Remember, immediately behind the hull the water begins to seek it's level, even on plane, so that at several inches behind the boat, the water's surface is above the lowest point of the hull.

ScottM · #5 04-23-2007, 02:42 PM

Quote:

The boat is a 1985. Was the 25 inch transom standard then? Were 30 inch motors even available then?
Thanks

My father's '82 Sceptre was factory-rigged with twins on a 30-inch transom. If the boat was factory-rigged for a single, it would have a 25-inch transom. I don't believe 30-inch motors were available back then, but in a twin setup, the transom has to be 30" because the (2) 25" engines are set outboard of centerline.

Fr. Frank · #6 04-23-2007, 05:55 PM

The factory twin setup on the early 80's SC was a 25" transom, and twin 20" shaft length motors. I just sold a '74 Tsunami with a 25" transom (actually 26 1/2") that came with twin 140 hp 20" Mercury motors new, and was later re-rigged with a single 225 Johnson with 25" shaft.

In 1984, I rigged a Seavette with twin 235 Evinrudes, and we used Second Effort prepped 20" shaft motors. WFO was 77 mph.

As far as I know, the pre-'88 SeaCrafts were not available with 30" transoms.

ScottM · #7 04-23-2007, 08:57 PM

Fr. Frank,
My father's '82 was changed over to a 25" single back in '90 or '91 ('89 225 Evinrude) and the transom was notched 5" to accomodate it. He now has a 25" 225 Yamaha on there. Perhaps a 30" transom was an option back then?

This pic gives you a shot at what his transom looks like.

Fr. Frank · #8 04-23-2007, 11:03 PM

Quote:

Perhaps a 30" transom was an option back then?

Must have been, for twin 25" shaft motors.

I know the first regular 30" shaft motors were no introduced until the '86 3.4L Mercurys. Prior to that, you had to buy an extension kit to get a 30" motor. OMC intro'd a 30" shaft the next year, in '87, and I think it was initially available only on the V8s, but I'm not sure.

As I think about it, I remember we notched the transom on a 25' Robalo CC that had twin 115's and put on a single 25" 235 EverJohn engine back in '84.