how fast should i be able to go?

[opposedtwin]

I took my 12 foot crestliner out on Tuesday (IN WISCONSIN!!) and achieved 21 mph. it’s a 2 cockpit runabout with an manual start 18 hp Johnson. just me in the boat (170 lbs) and my folding ducktwin back up motor. I was running a Michigan AJC 417 2 blade brass prop (what a beautiful prop: 9 1/4 x 12).

I believe anti-cavitation plate is a bit low. it’s 4-5 inches below the bottom of the boat. I’m planning to remake the transom this winter and raise it significantly. would addressing this issue gain me any speed?

should I have been able to go faster? I’d love to, but I believe my motor was running tip top. I feel like this is the perfect motor for this size of a boat. I have run others up to 30 hp and it can get a bit squirrely.

scott

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[RICHARD A. WHITE]

That aint no Merc…… I got 22+ out of my Wizard Super 10…supposedly just a 10…. 14 Starcraft rated fr 35 hp, I am over 250 with full tank of gas as well.

It is made for cruising, not racing..Want speed? Go to the dark side.. On a side note, I am rebuilding one of those very motors at this moment. Won’t be till spring but I will GPS the Johnson top see if any difference…

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[fleetwin]

Well, raising the engine, and perhaps trimming it out a bit, should help take advantage of that nice prop. The 12" pitch prop might be a bit much for that engine though, kinda tough to judge without a tachometer.
PS- What a beautiful rig!

[pappy]

Sitting up in the bow will definitely limit your speed due to wetted surface. Place your steering into the aft deck and you will make a very significant improvement.
My Model R with the 18 runs around 30-31 and my 15’6" fiberglass Gheenoe runs 27 with the same engine. Same prop you have.

GHEENOE

MODEL R (note steering position)

[20mercman]

My son purchased what looks like the same boat this summer at a camp near Wisconsin Dells. His boat is a Crestliner Commander 12 with the dual cockpit. We have only had one chance to put it on the water, and we were very pleased with the overall seaworthiness of the boat. It handles waver like a much larger craft. We really didn’t get much of a chance to really check it out, but it was our opinion that it was slightly slower than our 1979 14′ Lund CT-14. We ran a Mk-20 on it, and it ran very well, just a bit harder to plane off, and not quite the top speed. The hull still has a ton of loose rough paint on it, and that may add a significant amount of drag, but who knows. Over all, we were very pleased, but are trying to decide where to mount the steering position. I think we have settled on an aft control just so you can reach the motor easier, and not need electric start. We plan to run Mk-20’s & 25’s on it as well as some of our 200’s. Honestly, it felt like we should drop a pitch, compared to the Lund. We plan to strip the exterior and see how that does. The hull is built like a tank, very well built boat, and there is not a bump in it.

Where did you find the windshield for yours?

Steve

P.S. Where in Wisconsin are you?

[opposedtwin]

Hey Steve, I’m in Madison. The windshield was on the boat when I bought it. It has a crack which has been "surgically repaired"-I’ll post a pic when I get home tonight. You could probably use mine for a pattern. It’s just a cut/shaped piece of plexiglas. I think I met you and kevin(?) at the oconomowoc meet last spring.

Richard: funny you should mention the dark side. I have a few mercs (25s, 50s and 55/58s), which I’m planning to have water ready in the spring. We’ll see how that goes and post results.

Fleetwin: I agree. I’m hoping to have the height problem fixed in the spring. I will get a small tach and see what that tells me.

Pappy: I have seen your R videos and have been inspired by them. I got 2 R models this summer and found a steering deck for one. I will have a chance to run it next spring. I have considered moving the wheel to the rear cockpit. It might be something I try. If I don’t like it I can always change it back, right?

Thanks for all the feedback guys!

Scott

[pappy]

I think Randy in Tampa has the same hull as you with a rear steering set up. Much better performance. He ran a PO on his last time. In my experience with three different engines on my Gheenoe (18hp, Speeditwin @22hp, and a PO) they all ran around 27mph with the same load.
I think Randy was running better than your speeds pretty easily so you have something to look forward to.
Fleetwin is correct on raising the engine but the biggest bang for the buck will come with moving the steering back and setting the trim to free up the hull.

[opposedtwin]

quote fleetwin:

Well, raising the engine, and perhaps trimming it out a bit, should help take advantage of that nice prop. The 12″ pitch prop might be a bit much for that engine though, kinda tough to judge without a tachometer.
PS- What a beautiful rig!

hey fleetwin,
when you say trimming it out, are you referring to the position of the motor relative to the transom? based on the first pic I posted in the original thread, would I have to bring the bottom of the motor closer or further away from the transom?
thanks,
scott

[fleetwin]

Bringing the motor (exhaust housing/leg) further away from the transom is what I am saying when I say "trimming out". Try moving that trim rod/pin one notch out (farther away from transom) than it is now. Doing this will raise the bow of the boat out of the water with less friction.
Like Casey says, your helm set up may in fact be too far forward, making it near impossible to do this. You will know when you have trimmed out too far if the engine ventilates excessively, especially on acceleration, and if the boat porpoises (bow slaps up and down at high speeds) excessively.
Again, it would be nice to get an RPM reading at WOT now, to get a better idea if your engine is operating in its designed power band. Look at the transom ID plate, it should give the RPM range at WOT. An engine with a larger pitch prop, like yours, that is lugging, will not perform optimally. Let’s think of this in terms we are all familiar with. Let’s just say I am cruising along in my car at 35mph in fourth gear and suddenly have the need to pass another vehicle. What happens if I leave the gearbox in 4rth gear and stamp on the gas? Exactly, practically nothing. I would have to downshift to 3rd or 2nd gear in order to get the engine RPM up to where it can develop the power needed to effectively pass the other car. Think of propeller pitch as the various gears in your transmission. An over simplification, absolutely. Outboard motors do not have variable pitch propellers (like our auto transmissions). Furthermore, boats do not glide alone easily like autos, there is always a great deal of friction, consider what happens if your engine cuts out completely at WOT, people are tossed around in the boat and could be tossed into the water.

[billw]

My experience with 18s has been that those two-blade props only work well under the absolutely lightest and most drag-free, conditions. I’d put down money that says a standard 9 by 10 on your boat, without any modifications of transom or steering position, would give you a mile or two better. If you get lucky and can find a 9 by 11, by all means try that, too. At any rate, it would be worth a try, in my opinion, before you start having to deviate from stock design….I know everyone is right about the mods being a help; but my preference is to always favor originality. Your opinions may vary. 🙂

I do know that 18s are at least capable of 30 mph, if all, including compression, is top notch. 18s with lower compression can be very deceiving, in that they will run fantastic, idle great…..but they just will lack top end speed.

(I don’t recall off hand what the fractional number is for the diameter is on the above props. "9" is a rough estimate. Could be "9 1/4," etc. But you get the idea.)

Long live American manufacturing!

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