23cc with twin yamaha f150's, numbers???

[23acrplanes]

I have had twins on my 1984 23cc for about 6 months now and I'm still playing with props and motor height. Has anyone on here already done this and can tell me the best setup?? And I don't have bracket.

As of now my numbers are

4000rpm 30 mph
4400rpm 33 mph

I get 6100 rpm but then I get a speed wobble and have to pull it back, so I don't ever get a chance to see the top speed.

[23acrplanes]

I rebuilt the boat last year, it was a lot of work. Lol

[23acrplanes]

By the way.... I had a 2005 yamaha f225 on it for about 3 months and could not stand it. It wasn't enough power, way too sluggish. I love the twins on this boat. It's a whole different beast.

[Old'sCool]

Can't help but that's a really sweet rig! Is the height and toe correct? Or have you tried different positions? My experience w twin little engines has been a little higher mount, a little toe-in, and start w 17p props if 3 blade.

[23acrplanes]

Originally Posted by Old'sCool

Can't help but that's a really sweet rig! Is the height and toe correct? Or have you tried different positions? My experience w twin little engines has been a little higher mount, a little toe-in, and start w 17p props if 3 blade.

I'm running 3 blade 17p props on it now.... I tried 3 blade 19p sws stainless props and it only turned 5200rpm wot.

[Old'sCool]

What exactly is "wobble"? Those numbers sound pretty good. Are you touching tabs down a bit?

[23acrplanes]

Originally Posted by Old'sCool

What exactly is "wobble"? Those numbers sound pretty good. Are you touching tabs down a bit?

Like the little speed boats get...."Wobble" starts when boat around 6000rpm and starts rocking back and forth gradually getting worse, to the point where I feel like I'm losing control of the boat. Every time I've ran the boat I've had some one with me so I haven't wanted to push it but so hard. I'm taking it back to beach for a few days of fishing so I will be able to get better numbers. I talked to ken with propgods and he told me try to trim thru the wobble, maybe I don't have it trimmed right for the speed.

[Bushwacker]

You're "speed wobble" is commonly referred to as chine walk! Deep V's create more lift as speed increases so the hull lifts higher out of the water at higher speeds, the effective beam becomes narrower, and you lose lateral stability. The chine of a 23 will typically be clear of the water at the transom at about 45 mph. If you lift the hull high enough, it'll tend to bounce back and forth between two sides of the V, so about + 40 degrees on a 20 degree deadrise hull! Had it happen on my boat once in a slight chop with a very light load at almost 50 mph! It's pretty high frequency, quite violent, and can throw you out of the boat if you're not hanging on! If your trim tabs are mounted out at the chines where they should be, lowering the tabs a bit should stop it. I would think it'd be less likely with twins, especially if you're running stern-lifting props like a Merc Mirage, BRP Rebel, or most any 4B prop.

Regarding motor height, the top of the AV plate is intended to be above green water when you're up on plane and fully trimmed out, so have someone else run the boat and look over the transom . . . if you can't easily see the top of the AV plate, the motors need to be raised to minimize lower unit drag. BTW, what's your min planing speed? Most folks don't pay attention to that when testing props, but it's important to be able to hang on plane at low speeds in rough seas. All the original Moesly designs with I/O's or ~300 lb outboards would plane at about 12 mph. The 23 isn't a Moesly design, so it probably can't plane that slow.

[23acrplanes]

Originally Posted by Bushwacker

You're "speed wobble" is commonly referred to as chine walk! Deep V's create more lift as speed increases so the hull lifts higher out of the water at higher speeds, the effective beam becomes narrower, and you lose lateral stability. The chine of a 23 will typically be clear of the water at the transom at about 45 mph. If you lift the hull high enough, it'll tend to bounce back and forth between two sides of the V, so about + 40 degrees on a 20 degree deadrise hull! Had it happen on my boat once in a slight chop with a very light load at almost 50 mph! It's pretty high frequency, quite violent, and can throw you out of the boat if you're not hanging on! If your trim tabs are mounted out at the chines where they should be, lowering the tabs a bit should stop it. I would think it'd be less likely with twins, especially if you're running stern-lifting props like a Merc Mirage, BRP Rebel, or most any 4B prop.

Regarding motor height, the top of the AV plate is intended to be above green water when you're up on plane and fully trimmed out, so have someone else run the boat and look over the transom . . . if you can't easily see the top of the AV plate, the motors need to be raised to minimize lower unit drag. BTW, what's your min planing speed? Most folks don't pay attention to that when testing props, but it's important to be able to hang on plane at low speeds in rough seas. All the original Moesly designs with I/O's or ~300 lb outboards would plane at about 12 mph. The 23 isn't a Moesly design, so it probably can't plane that slow.

Good info! I was scared something was wrong with my boat. Goin to run it now and try some tabs. What props is everyone running with this setup?

[Bigshrimpin]

wow . . . I'm amazed that twin f150's can't turn more than 17p wheels. I'll bet the motors are too deep.