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

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.

Another pic
 

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

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.

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.

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.

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?

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

I lowered them 2 holes because it was chine walking too much..... I will probably raise them back up. When I lowered it it def slowed the boat down quite a bit.

I saw 47mph today at 6100rpm with tabs in, and a heavy load.

You went the wrong way lowering the motors. when I was running 250's on mine the higher I moved them the better it handled. 68mph on gps ran smooth as silk.

Duane you're killing me!!!!! 68 mph is some serious pucker power!!

I've had mine at 51 mph on the GPS with perfect conditions and that was good enough for me!!! 68 mph on a 23' SeaCraft, let me think about that for a minute. I've been on a 17' Hydra-Stream at 108 mph and I told the owner just take me to the shore, I'll walk home.....

Been told there can be a big difference in the way a boat response to twins depending on what direction the counter rotating engines are located if they rotate inward or outward --- what works for the 23?

Mine had twin 250s on it with the previous owner. Not sure how fast it got as the chine walk was so bad you couldn't hold it to find out. Now I run half the HP and still get 40+ knots fully dressed.

Here's a pick of the twins.....

dayummmm........😱

When I originally set mine up with the 250's they were turning in. Way too much transom lift would dance on the Back end and would not lift the bow 10 mph slower. Don, we ran from the St Pete peer to the Gandy one day wide open, needed ac it was hot out there. Not a wiggle smooth as could be. Miss running them monsters but not feeding um

You need a set of stern lifting props.

I have a friend with a 23' SeaCraft "Savage" model which is basically a Sceptre that has had the windshield removed and a center console added. He runs that exact setup (twin Yamahas F150's) the boat seems ass heavy and sits at rest pretty deep in the water in the stern. Very noticeable, even with the weight of the cabin up front. He does have an Aluminum hardtop/tower though.

The hole shot is pretty strong, but not 2 stroke strong due to the weight. He gets about 50 mph at WOT which I think it pretty good. I don't know what RPM he is running at WOT. But based on the hole shot and the WOT, he might be a candidate to run a slightly lower prop pitch to help with the COG/weight so far back as his motors are mounted on a non-floatation bracket. IMO, its border line too much weight back there.

First the bracket, and twins, take into consideration the location of the fuel tank.if there is a well or storage bin forward of the console.tank is aft,batts etc....that boat is gonna sit a lot different than most.nice look but whats best for a 23

If you are chine walking at top speed you might want to have someone sit
near the bow and see if the weight up front cures it.

Denny hit it pretty well.
The lateral instability inherent in a deep-V hull with no flat planing surfaces is most noticeable in smooth water. Choppy water will actually give you a more stable ride. The hull rises up and tries to ride on what is effectually two points of contact: the keel line of the v-hull and the point mid-way between the two propellers which is the effective point of thrust.
Here's a couple of notes you may already know:
a) Having outward rotation on twins helps with stability and steering, but creates a bit more drag.
b) You want approximately 3/4" - 1" of toe-in for each 24" of separation of your motors.
c) Deploying your trim tabs slightly as speed increases creates two additional small points of stabilizing drag that actually reduce your speed only negligibly and stop/reduce oscillation noticeably.

As I said in an earlier post, I sold a 23' SeaVette back in '83 that the customer took to Frank Brown for rigging with twin 300hp 3.4L Mercs. It reportedly could hit 77 mph after tweaking.

Back in 1984/85, my own 23' Savage with twin Mercury 225's could hit 57-58 mph with the bimini down.

The twin setup works well on my 23' Tsunami. 175 twin mariners on a Gil bracket, CR prop on the port engine, set up with hydraulic steering. It's a different boat with the bracket setback. Trim tabs help the stern lift, as does working with gas tank centre of gravity forward as needed. Had to reinforce the transom / stringers with some angle bracing.