Yamaha F70 on a 20 MA?

[bumpdraft]

No, we did try that, but he could not keep up, so we hooked up again and just stayed that way. There were no waves to worry about. Maybe if we transferred all weight to another boat, it would have been better and I think that could be an issue on the 20. Keep a light load and put the right prop on and I think it would work.

[Fr. Frank]

I actually did rig 1 (one) 20' with an Evinrude 70 back in the early 80's. It could get the boat on plane but was clearly inadequate. But customer is always right, eh?

I think 85-115 hp is the right HP range for the 20' if you're worried about weight. Your F100 is a good motor . If you're getting airborne in the heavy chop trying running with the motor trimmed all the way down. Adjust your propeller torque tab for that configuration. Alternatively, and better yet, let me suggest adjustable trim tabs. Keep the nose down and it's much harder to get airborne.

The 20' was designed for a single 275-315 lb outboard, or in the case of some of the wide transom cut-out models of '68-73, up to twin 50-65 hp motors at 190 lbs each.

The very first Seafari I rigged back in '83 was a '69 re-rigged from its original twin 190 lb '69 Johnson 55 hp 3-cylinders to a single Mercury 140 ELPT inline 6 weighing in a bit over 300 lbs

[bumpdraft]

Originally Posted by Fr. Frank

I actually did rig 1 (one) 20' with an Evinrude 70 back in the early 80's. It could get the boat on plane but was clearly inadequate. But customer is always right, eh?

Just curious, was that motor rated at the crankshaft?

[doug7488]

I’ve recently repowered my 77 Seafari 20’ with a 115 Etec
I feel it’s borderline acceptable
If I had to do it over I’d go with a 150

[fishstu]

A 70 hp would get a SC 20 on plane if it is lightly loaded - pretty sure that the boat performance would be limited with say 4 guys with gear on board . I think the Mercury 115 hp 4stroke is a great fit for the SC 20 - I have 150 Etec on mine which can push the boat faster than I need to go.

[FishStretcher]

Fr. Frank- For some reason, I thought you rigged a 75 HP once, but I couldn't find a reference.


I noticed one of the recommended power options on the Mosely site was 80 HP for a 20CC and stated 35MPH top speed. But a 1400lb hull weight.


I don't run a heavy boat and was estimating the mass benefit of a foam transom and a 110 lb lighter outboard. I wish the 90 was a bit lighter, but it's not.

Originally Posted by Fr. Frank

I actually did rig 1 (one) 20' with an Evinrude 70 back in the early 80's. It could get the boat on plane but was clearly inadequate. But customer is always right, eh?

I think 85-115 hp is the right HP range for the 20' if you're worried about weight. Your F100 is a good motor . If you're getting airborne in the heavy chop trying running with the motor trimmed all the way down. Adjust your propeller torque tab for that configuration. Alternatively, and better yet, let me suggest adjustable trim tabs. Keep the nose down and it's much harder to get airborne.

The 20' was designed for a single 275-315 lb outboard, or in the case of some of the wide transom cut-out models of '68-73, up to twin 50-65 hp motors at 190 lbs each.

The very first Seafari I rigged back in '83 was a '69 re-rigged from its original twin 190 lb '69 Johnson 55 hp 3-cylinders to a single Mercury 140 ELPT inline 6 weighing in a bit over 300 lbs