1986 21 Mako twin Honda 50 four stroke How fast?

[captmarkhd]

Hey Guys, I am looking at buying a 1986 21' Mako (2500lbs dry) in central america that is powered by (2) 2003 Honda 50 four strokes. The seller is telling me that the boat will top out in the low 30mph range. This seems fast for the power plant. Has anyone had any experience with a similar set up?

Thanks mark

[jay_merrill]

I would expect something more like high twenties with that setup and that would be at relatively light operating weights. If one engine quits and the boat has to be brought home on the other, forget planing - you'll come home at displacement speeds.



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[captmarkhd]

Hi Jay, that was closer to my thinking as well. I figure that I will be loaded with people, fuel and gear at about 3600lbs. Also this boat had a transom/hull extension done to help carry the twins stretching the boat to 23'. I think the added water line should help carry the weight better. I have 0 experiences with twins, only singles. Correct me if I am wrong but it is my understanding that twins are not as fast up top as a single with the same hp because of the extra drag but carry weight a lot better because of the increased torque and also the decrease in prop slip. I have had boats that would top out close to fifty but I found that in real world conditions, offshore, without abusing the boat and people I only cruised them in the low 20’s. I believe that most people way over power there boats (just my thoughts). I do think that this boat is a little under powered, twin 60’s or 70’ would be perfect. I hope that the boat will cruise in the low 20’s loaded at 3600lbs. Any thoughts?
Thanks, Mark

[Home Cookin']

The old mako's are good hulls.
But that's an odd rig. You'd typically want about 150+ on it. Most boats with twins nowadays run larger motors; in the 60's they might rig twin 20's even. My theory is that back then, the motors were so unreliable you needed a spare!

So if having a spare is important, twins would make sense. If you don't need speed and gasoline is expensive, you might want small motors (remember that adequate power is a safety factor, too). Those are new expensive motors. Talk to local boaters to see if that is not unusual down there and why they would rig it that way.

[jay_merrill]

I'll offer a few more thoughts ...

Yes, twin setups of a given HP will yield less top speed than a single setup of the same total HP. You are correct in assuming that drag comes into play. From the standpoint of pure efficiency, the twin installations don't match up to a single engine installation - you will burn more fuel, have higher maintenance costs, etc.

I also agree that many people are way too focused on speed, especially when it comes to a hull like a Mako, which is intended for operation in water with some waves/chop. Simply put, the boat isn't going to be operated at 30+ mph most of the time.

I do think this boat is underpowered for most people's needs, though. It is probably rated for about 200 - 225 HP and most people would probably put at least 130 HP on, it in a single engine setup. As a twin engine installation, I would be inclined to put a pair of 90 HP two-stroke engines on the boat and more, if the engines were four-stroke. My reasoning is that a 90 HP two-stroke would probably hold a plane in most situations, if the other motor was out and tilted up, but a four-stroke would most likely need more size to develop the torque necessary to do that.

I'm not faulting the seller for powering his boat the way he did, simply because the boat most likely met his needs at the time. If he wasn't looking for high overall speed and was content with the idea that a single engine trip home could be slow, there is nothing wrong with what he did. The question, however, is whether or not the boat will meet your needs, should you buy it.



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[captmarkhd]

All good advice, these were my thought as well, I just wanted to get some re assurance. The reason why people will put twins on boats down there is 100% redundancy. there is no vessel assist or Coast guard to speak of, your on your own. Fuel cost is another factor as well @ 5.00 per gal. Your right, The questions is what will I be happy with? I would be happy if the boat would cruise at 20-22mph,with a loaded weight of 4,000lbs at about 5,000 rpm, am I dreaming?

[dingbat]

All good advice, these were my thought as well, I just wanted to get some re assurance. The reason why people will put twins on boats down there is 100% redundancy. there is no vessel assist or Coast guard to speak of, your on your own. Fuel cost is another factor as well @ 5.00 per gal. Your right, The questions is what will I be happy with? I would be happy if the boat would cruise at 20-22mph,with a loaded weight of 4,000lbs at about 5,000 rpm, am I dreaming?

I think your dreaming. I had a Grady 21 that weighted about the same. It had a Merc 175 2 stroke on the back. At cruise, 4200 RPM was 22-24 mph depending on the conditions. Can't see doing the same with almost 1/2 the HP.

If you want real fuel efficiency, look at a Cat. I fished a 28’ Pro Kat over the weekend that had twin 115 HP 4 stokes on the transom. It cruised at 25 knots. A 21' Kat with twin 50HP would fly