Larger Single Engine versus Twin Engine

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-scott-

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I have a Mako 252 with a Honda 225 four stroke. Top speed is 36 mph with half tank of fuel. The engine is really not large enough to give this hull the needed power.I am contemplating twin 150's. how can I best determine the performance of this combo in terms of expected top end speed? Also, can you shed any light on performance characteristics of a single engine at a specific HP versus the performance of a twin engine set up with a similar combined HP?
 
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swist

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Re: Larger Single Engine versus Twin Engine

No specific data, but some observations - you are adding 75hp but also increasing the weight on the transom considerably (assuming these are carbed two-strokes) I am guessing you are adding 250 lbs at least. This is going to eat some of the 75hp - your net gain per dollar spent could be very little. I would think a 250 might be a more attractive alternative.<br /><br />Of course you may want two engines for redundancy, which is a different set of parameters altogether.
 
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phatmanmike

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Re: Larger Single Engine versus Twin Engine

or ditch the heavy honda and get something a lil more weght friendly... how bout twin efi 2strokes
 
JB

JB

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Re: Larger Single Engine versus Twin Engine

Twins will also double the drag. My guess is that you will need more than 300HP in twins to get a noticable gain in performance over your 225.
 
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BF

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Re: Larger Single Engine versus Twin Engine

drag?? that doesn't make sense to me. If the engine is producing thrust/propulsion, then it is already itself overcoming the drag from its LU in the water. A 150 hp will produce way, way more push than drag (net effect is propulsion). So I don't see how drag fits into the equation... (but then again I've never had twin OBs either)<br /><br />Brent
 
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ED21

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Re: Larger Single Engine versus Twin Engine

I don't know anything about twins either, but it seems the more you have hanging in the water the more drag you have. What it is & how much it effects performance I don't know.
 
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DJ

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Re: Larger Single Engine versus Twin Engine

I'm with JB on this one. Drag is a real issue.<br /><br />The twins will definetely outperform the 225 as far as low end push goes. The top speed won't be a whole lot different.<br /><br />What is the boat rated for?
 
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swist

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Re: Larger Single Engine versus Twin Engine

As far as redundancy goes, there's one school that says that twins don't add a lot over a well maintained single engine, many of the problems being fuel problems what will hit both engines.<br /><br />But after reading all the things that can go wrong with outboards, even new fancy modern expensive ones, I'm not so sure.<br /><br />Of course if we had topics on how well our outboards ran, maybe a more balanced picture would emerge. But it wouldn't make for very interesting reading.
 
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Solittle

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Re: Larger Single Engine versus Twin Engine

swist wrote "As far as redundancy goes, there's one school that says that twins don't add a lot over a well maintained single engine, many of the problems being fuel problems what will hit both engines."<br /><br />I am not of that school as I run a pair of 110 hp OMCs on my 23' CC & have had to get home on one a couple of times in the past 10 yrs and my engines are well maintained.
 
dingbat

dingbat

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Re: Larger Single Engine versus Twin Engine

That boat is very under powered with only 225HP on the back. The twin 150's would be nice but I'd check on see what it would cost to go with twin 175Hp and but a little pizzazz back into that boat. With that said, I personally wouldn’t do it just for the speed simply because it’s few and far between that I actually get to run at WOT. On the other hand, I would opt for the twins to put a little life into the boat along with the added security of a second engine to limp home on if need be.
 
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DJ

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Re: Larger Single Engine versus Twin Engine

I like twins too, for many reasons, as stated.<br /><br />That is a heavy boat.<br /><br />That's why I ask, what is it rated for?
 
S

-scott-

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Re: Larger Single Engine versus Twin Engine

THe 98 Mako 252 is rated for 300HP. As some of you have stated, two shafts will have more drag than one, thus some of the increase in HP will be given up to overcome this additional drag. That is why I am curious as to whether there are any published stats on this. I would imagine the marketis not far from a 300HP 4 stroke, which is my preference over two stroke. Thus, I am trying to assess differences in performance for twin versus single at same HP rating.
 
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Captn Dave

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Re: Larger Single Engine versus Twin Engine

I have a 1978 25" Mako and with a 225 HP Johnson.<br />Simply put, the boat is a dog. Don't get me wrong, I've been running this set-up for 10 years and have been getting by with it okay. But when I repower I'll either go with a single 250, or if I can find the right combo, twin 150's. I have known guys who have had the same boat with twin 140's and twin 150's and that set-up performed far superior to mine.<br />I've gone fishing with a friend who has a 25' Grady White with twin 150 Yamahas. With four people on board and I think something like 175 gallons of fuel, we could cruise at 30 kts at 4300 rpm.<br />In my humble opinion, twin 150's is the perfect choice for power and cost for that size boat.
 
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quantumleap

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Re: Larger Single Engine versus Twin Engine

I don't believe the equation is as simply as merely adding the rated hp of the twins together to compare to the hp of the single OB. You have two drives functioning together to provide much more low end power than a single motor. Two props = more bite out of the hole plus less slippage at wot.
 
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tee-boy

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Re: Larger Single Engine versus Twin Engine

I think Quantumleap hit the nail on the head.
 
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tee-boy

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Re: Larger Single Engine versus Twin Engine

Of course you have to consider that the single engine can turn a larger prop than the twin engines.
 
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Dhadley

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Re: Larger Single Engine versus Twin Engine

The twins should turn more prop than a single.
 
G

GeeFrankk

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Feb 24, 2004
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Re: Larger Single Engine versus Twin Engine

I know what the orginal post is, but why not consider a newer boat which would be lighter than the mako. The 70 and 80's model mako were laid up heavy with alot of glass and are damn near steel which equals weight. One single large hp motor w/a kicker would be the way to go. With what the newer motors cost, seems like this would be the ticket.
 
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youngboater

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Re: Larger Single Engine versus Twin Engine

I'd upgrade to the 250 or a 275 Merc. Verado (I'm not sure if anybody else makes a 275). Then buy a kicker motor. Seems like the best way to go. You won't be stranded if the big boy breaks down. That is how I would do it. Just my opinion
 
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