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Yamaha F70 on a 20 MA?
Toying with the idea of a rehab- cleaning the carbs and fixing the tilt/ trim on my Yamaha F100 and selling it.
Then finally fixing the transom on my 20 MA with coosa and divinycel. A Yamaha F70 with EFI is 253 lbs. Versus 363lb or so for the F100.That and a foam transom, and needing and carrying less fuel has me wondering. I think this is a question for Fr Frank. This boat is too small and light to go fast in a Buzzards Bay chop. I always try with the F100 and never can air it out. This may astonish some of you, but it gets airborne too often with just a F100. I can't get to 30 statute MPH on any sort of regular basis. This would never work for a Florida boat, I know. But a new, light EFI engine is appealing. And kind of fits with the Mosely vibe of "light is right". No raising decks, no worrying about flooded scuppers, no worry about center of gravity... |
i had a f115, the thing was a dog. had no balls.
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A long time ago, I was fishing/camping with several friend in the Keys. One of my friends had a 22Aquasport with twin 70s. One of his motors quit on him and he couldn’t quite get the boat to plane going home. We threw him a long rope and we cruised the 25 miles or so back to dock. I think if he could have ditched the dead motor and maybe put a different prop on it, he could have made it without any help.
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Better have more and not need it than need it and not have it
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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.
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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 |
It's a 1000cc motorcycle engine that works great on the 16', to maybe an 18' "technical skiff" that weigh nothing......on a 20' SeaCraft get real!!
Too blunt? Sorry, Yamaha is known for pushing the low end of the 10% variance on their engines' HP ratings! |
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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. Quote:
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70 on 20 MA
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 |
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Gomer Pyle : He hopped up an old V8 engine, put it on his rowboat. That thing'll do eighty. Now that's fast on water. I mentioned the Aquasport experience because it was a bigger boat. From what I looked up just now, it was about 600 pounds heavier than the 20’ SeaCraft and it was almost there with a dead engine weight on the rear. Obviously, it’s not going to be a speed machine, but maybe doable for what one wants to do. |
Bumpdraft-
Drat,I just lost a half hour of typing. Thank you for confirming and clarifying your observation of the Aquasport I was trying to determine the weight of that hull. Based on your data, I am still considering this. Quote:
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I'm on the skeptical side myself on this, but how about keeping both motors for now, getting the boat fixed up and trying it out with the 70? If you like it, THEN sell the 100. If it's too much of a dog, put the 100 back on and sell the 70. I know it's a bit of a pain noodling with rigging, but the peace of mind of "knowing for sure" would be hard to resist for me. Eventually resale with a 70 would also suffer, as most folks are gonna look at that and say "Needs a bigger motor."
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I have thought about doing just this. I expect that the F100 with new tilt/trim, water pump and clean carbs is worth something. Even with a largely brken tilt/trim, it was fine for 2 weeks of vacation.
At present, I run the F100 with a hydroshield (under skeg wing). Which lifts the stern but must cost something in drag. With a lighter motor, I may not need this. I run a 15P prop at present with a 2.33:1 gearcase (same ratio as F70). It's an expensive experiment. But I am interested in the challenge. |
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The Yamaha 115 SHO is the lightest per HP you MAY/MIGHT/MAYBE have a shot at. 386 in 25". I compared weights of the big 3 recently in four stroke. The only caveat is Merc only advertises their short shaft which would be 20". In my opinion, the Merc 150 and Suzuki 140 shine pretty bright at this time. I have never owned either.
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I would not want anything smaller than a 140 on an 18, 150 on a 20. My 18 will do 39 mph wot. I'm sure I could tweak it, prop pitch, etc and squeak a bit more out, but 39 in an 18 is flying to me!
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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.
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Ok, hold the presses FishStretcher. I called my friend to verify the story. He was the one that owned the Aquasport, with a 200 on it, sometime in between owning a 18 and a 20 SeaCraft. Our other friend that broke down with the twin 70s was actually in a 20' Robalo, still a heavy boat.
We were reminiscing about the old days and the marine science classes we took at Miami Dade college. Our class used two 22' Aquasports, powered by twin 55 hp Johnsons, borrowed from UM. There was about 12 or 13 of us on the two boats and we visited Fowey rocks lighthouse a little ways offshore. The keepers of the lighthouse showed us lenses and other gear. Twin 55s on heavily loaded boats and no problems. Nowadays nobody would think to power a 22 with 110 hp. |
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It runs 36 mph at WOT lightly loaded and trimmed out. Cruises best at about 4000-4200 rpms at 24-25 mph. Holds plane down to 11-12 mph without trim tabs but with Hydro-Shield under the prop for stern lift. Unless you really feel the need to travel at 40 mph+, the 90 Etec is fine for the 18' and light weight. (And yet my 1987 '18 by CSY is actually placarded for 200 hp max instead of the later Tracker models and earlier SCI models which are rated at either 140 or 150 hp, although I have seen an '86 CSY 18' rated for 175 hp) |
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The old OMC 150 eagle series was a bit of a middle finger to Merc as it turned 168 at the prop. I can hold plane at 3k and 12 mph not kts. My `89 Slacker 20 hits 43 wot as propped. Not for wot. The Seafari has a bit more weight forward. My CG plate lists 235 max HP and the transom is 2 3/8 thick from the factory. |
I would find you a 2 stroke 90. I think the etec would be great.
I have an old old Tohatsu 90A carb motor on my 18 and have been shocked at how well it performs. Planes quickly, 'WOT is about 32 and gets 3.3 mpg average. Its also been crazy dependable. I like the simplicity of the 2 strokers. |
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