Twin 9.9 hp outboards for HP restricted lakes

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chuck99z28

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Please be kind. I've been looking at a boat to share between some local HP restricted lakes and a local tidal river (Potomac). I'm somewhat limited to a boat in the 15-17 ft range due to a single car garage. 78 inches wide by 22 ft. I'd prefer a side console. Decent budget.

Why doesn't anyone discuss putting two 9.9 hp engines on a boat that is rated around 40hp which many of these boats are?

For example, the Mercury 9.9 weighs a bit more than 100 pounds, and the Mercury 40hp weighs 260 pounds. It would weigh less.

I know twin 9.9 hp engines isn't the same as a 40hp. But wouldn't it be worth it to use one on the HP lake, and two on the river?

What about a 25hp and a 9.9? Thats about the same weight as a 40 hp engine.

Is it just not worth the expense? Not enough juice for the squeeze?

Addition: I just realized this post is probably in the wrong section. Sorry.
 
Just do what everybody else does and put 9.9 stickers on your outboard. Just go slow on the lakes. If you was to run twin outboards one needs to spin clockwise while the other needs to spin counter clockwise.
 
I've thought about this before. I've spent a LOT of time in bigger patrol boats with dual motors. The maneuverability you get with duals is awesome. I don't have the money to spend on my personal boat that was spent on the patrol boats I've run but I would LOVE to have a 16-18', center console, with dual 15 to 20hp (maybe even 30) motors (even more awesome if I could have them both mounted on a single hydro/electirc jack plate :-D ). I could go just about ANYWHERE and do ANYTHING I would ever want to do in a boat with that setup. As stated above though, the lower units have to spin opposite. I don't know if manufacturers do that on smaller motors. It was a moot point for me cause I didn't have the money for 2 motors. I would love to see pictures if anybody has done it though so I could live vicariously through them.
 
Oh, ok. They turn is opposite directions. Something I learned today thanks to you.

Expense and finding small motors which do that is probably the reason then.
 
It has been done before and looks cool, the biggest draw back is the drag of having 2 lower units in the water. On a small boat I wouldn't worry about counter rotating props.
 
Dual 15's, or 20's on an 18' center console would be severely underpowered. A single 40 would outperform it and 40hp isn't enough for an 18' CC. Duals don't come into their own until you reach the higher horsepower ranges.

As mentioned earlier the increased drag of two lower units robs you of a lot of performance.
 
lckstckn2smknbrls said:
It has been done before and looks cool, the biggest draw back is the drag of having 2 lower units in the water. On a small boat I wouldn't worry about counter rotating props.

At one point I owned both a 3hp Evinrude and a 3hp Merc. One day for fun decided to put both of them on my little 12' jon boat. Snugged them down so you could take your hands off either one and they would still run straight. So I started up one and got it running full throttle, made about 7mph. Fired up the other one and got it running full throttle, looked at the GPS and I was at 5.5mph. Took the other motor out of the water and jumped back up to 7mph. Either motor ran 7mph alone, but 5mph in tandem. I'm sure you guys can tell me why, but I reasoned that if both screws are turning about the same speed, you aren't going to get any more thrust but will see more drag? It was interesting. Do dual screw boats go faster or just have a better hole shot?
 
Lowe 2070 CC said:
Dual 15's, or 20's on an 18' center console would be severely underpowered. A single 40 would outperform it and 40hp isn't enough for an 18' CC. Duals don't come into their own until you reach the higher horsepower ranges.

As mentioned earlier the increased drag of two lower units robs you of a lot of performance.

Just to be clear, I wasn't talking on a 18', center console, glass boat. I was talking a 16' to 18' center console jon boat. The center console jon would be significantly lighter. You still think that would be underpowered? And on my hypothetical example, wouldn't the motors being on a jack plate help alleviate some of the drag on the lowers by letting you optimize their height on the move? But I think I've hijacked, sorry. I'll be quiet now.
 
jethro said:
lckstckn2smknbrls said:
It has been done before and looks cool, the biggest draw back is the drag of having 2 lower units in the water. On a small boat I wouldn't worry about counter rotating props.

At one point I owned both a 3hp Evinrude and a 3hp Merc. One day for fun decided to put both of them on my little 12' jon boat. Snugged them down so you could take your hands off either one and they would still run straight. So I started up one and got it running full throttle, made about 7mph. Fired up the other one and got it running full throttle, looked at the GPS and I was at 5.5mph. Took the other motor out of the water and jumped back up to 7mph. Either motor ran 7mph alone, but 5mph in tandem. I'm sure you guys can tell me why, but I reasoned that if both screws are turning about the same speed, you aren't going to get any more thrust but will see more drag? It was interesting. Do dual screw boats go faster or just have a better hole shot?


It would make sense to me, if one motor was providing more thrust then the other, that the lessor of the two would be getting dragged ahead slowing down both motors. If both motors were the same, same prop, everything and you could at least get the RPMs close then I would expect something more out of two. Not sure how much more.
 
It's isn't that twin outboards turning the same direction would cause the boat to go in a circle. It needs to spin in opposite directions because of cavitation. The props can't get enough smooth water over them.
 
dutyranger said:
Lowe 2070 CC said:
Dual 15's, or 20's on an 18' center console would be severely underpowered. A single 40 would outperform it and 40hp isn't enough for an 18' CC. Duals don't come into their own until you reach the higher horsepower ranges.

As mentioned earlier the increased drag of two lower units robs you of a lot of performance.

Just to be clear, I wasn't talking on a 18', center console, glass boat. I was talking a 16' to 18' center console jon boat. The center console jon would be significantly lighter. You still think that would be underpowered? And on my hypothetical example, wouldn't the motors being on a jack plate help alleviate some of the drag on the lowers by letting you optimize their height on the move? But I think I've hijacked, sorry. I'll be quiet now.

My 1650 Xpress always felt underpowered with a 40, but it did OK (really needed a 60). I'm running a 20' Center console jon now with a 115 and wouldn't go less than a 90. That 18' will likely be rated for a 90 and you're looking at running less than half of that plus adding a second lower unit for double the drag. My bet is that you couldn't get the 18' CC to plane with two 15's on it.

I have a 2060 workboat forward console jon with a Merc bigfoot 60 right now that does OK but struggles to plane with a heavy load.

Two motors doubles the amount of drag and the parasitic loss from the props fighting for clean water to bite adds to the trouble. If you need 300hp+ or go way offshore, then duals may be the answer, but one 40 beats two 20's all day.
 

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