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Just curious, what exactly is causing the phenomenon where at high speeds when you drop the trim down, or go to high speeds and don't trim the motors up the boat rolls. My 22's did it and of course i learned long ago to trim the motors up as i but on more speed. Sunday during a speed run on my new motors on the 25, trimmed the motors down looking for the sweet spot, and at almost 50 MPH the boat rolled hard to the right.

Just curious what factors are in play to do that. It was a pretty aggressive roll. I would assume the only thing that would be effected would be the bow height, so whats giving the hard right roll?

Duf

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My 15' 70 hp Yamaha was doing that because not enough of the trim tab was in the water while on plane. It was pulling hard to starboard when I had the motor all the way 4 holes up.

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Well, i don't have trim tabs and its a very aggressive roll, so just wish to understand the physics that are causing it. I know its going to happen, got that, but am interested in the whys!

Duf

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I don't know if this is the same but I got a boat once that did that because it had the wrong size prop. But if I remember right the boat would pull the entire time while on plane.

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I'm actually talking about the adjustable tab on the antiventilation above the prop.

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Not sure either gents, though i'm sure someone on here does. It's a very aggressive roll, and i'm sure someone, maybe with a 22 or larger Whaler has dealt with it.

duf

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Duf, is it an occurrence you can predict and possibly video? I'm curious to know a which speed (less) that it does not happen. What type and brand, model steering system do you have? Do you have a picture you can show directly behind the boat facing the motors, and maybe a pic or description of the planing surfaces on the hull at play here?

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Duf -- What you experienced is very similar to a sailboat broaching.

When the bow is forced down into the water, as it might with the motors trimmed in with good stern lifting propellers on the motors, the buoyancy of the bow wants to float upward, but it is does not do so in a stable fashion; as soon as it tends to one side, the bow will accelerate in that direction. This is exacerbate by the high speed.

The same thing can also happen with twin outboards that have too much toe-in. I doubt that is your problem given the Whaler Drive but you might check it just to eliminate that possibility.

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Duf,

The situation you are referring to is the work of gyroscopic rotational forces from the motor forcing the hull over. This problem is the most noticeable and common when operating a single engine vessel with the motor trimmed all the way in, thus forcing the bow to "plow" while on plane.

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I just experenced the same on my seatrails, I attributed it to the rotational torque of the prop without enough trim as the bow came down and with the torque of the prop the left chine dug in and tossed me and to the right. My conclusion was improper trim at the speed I was going. Just my observation.

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In spite of having a fast 18 Outrage, and a fast 25 Outrage, I have never experienced this condition.

My guess is that the situation is "bow steer". Mercury says:" Trimming engine in, in excess, can cause the boat to veer to the left or right (bow steer). They also say it can cause undesireable and unsafe steering conditions.

With those high torque engines at high speed you might have driven the bow into the water too much, too fast. The situation could be exaggerated if the engines are mounted too low. You should be up in the 4th set of holes at least, maybe the the 5th (all the way up).

Check your engine bracket design. It may have a provision for a tilt pin stop to prevent excessive trim in, like the older design engines had. A 10" long 3/8" SS bolt can be used (at least on mine it can). This will prevent excess/unsafe trim in, hence preventing the rolling you describe.

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It's not a whaler but my 25' boat with an I/O will do this on a plane, outdrive trimmed all the way in and the trim tabs too low. It makes the bow dig and it takes an aggressive turn.

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Duf I assume you have counter rotating setup with the two motors? It's what Tom said broaching or like finnegan said bow steer. A very dangerous condition as the boat can really roll over forward when the bow suddenly digs in instead of just rolling to on side. You must adjust trim and motor mounting height to keep that from happening when you want to keep using the high torque/HP motors you have.

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As already noted above, the hard pull to the right (not left) when a single outboard is trimmed all the way down/in is the result of gyro rotation force caused by the "prop rotation" and hull drag. This is NOT the case for twin counter-rotation outboards are used as they are counter acting the gyro rotation torque. The off-set to this gyro rotation torque is also as mentioned in another post above, "adjusted" using the trim tab found under the anti-cavitation plate above the prop. Turn the "back" of this trim tab in the "opposite" direction (left) as your pull is to the right.

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I agree with the latest, I think its time to get some tabs. Keep the drives high and optimize with tabs. I have a ton of experience with 20'+ boats with single, twin, and triple engine boats. My latest CC had 24" K-Planes (snuck a pic on the bottom of my PP temporarily). I also noticed on you personal page that photo #8 down, shows your boat under idle power, engine turned slightly, and you boat appears to be leaning. Is that an optical illusion? Fuel shift? Boat not loaded and too buoyant with a high CG? Did you ever notice that happen?

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When I ran a 25' CC Mako with twin 225's on it professionally, I would run the engine trim up to the point where it almost cavitates. It was at that point where the bow has risen enough at full power that it's wouldn't hook to the right. This was 20+ years ago.....but I'm sure the same principle still applies.

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I own a 25 foot Whaler with twin 150 HP Mercurys on it. I've run it with both motors as standard rotations and then converted one to counter rotation.

"Gyro rotation forces" have nothing to do with what Duf is describing, nor do the trim tabs on the motor (which Duf's motors do not even have)

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Duf,

How rough was the water when this happened? Was there a following sea? Since you were running 50mph my guess is you were in the ICW with small chop. I have not experienced this in my boat.

Perhaps there is too much weight between the center console and the leaning post...just kidding. Glad to hear you were not hurt.

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Tom, To clarify, I was speaking about transom mounted hydraulic trim tabs. Those are independent of the drive.

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James -- Yes, understood, others were not. No place for trim tabs on a 25 foot Whaler with Whaler Drive.

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James, the photo's you are looking at are of my 22 Whaler, not my 25 with Whaler Drive. I keep saying i will update my Personnal page :)

CES thanks for the congrats!

John, bite me i went on a diet, so i'm going to tell Trish, you blamed her weight!

All good info, and i appreciate everyones insight. As i stated earlier, i understood it would do it (at some point), but wanted to understand why, not just that it would. Opinions are pretty centered, its the bow driving down, which in a sense, make the boat stand on its nose, though its not noticeable. One thing i may do, other then the stopper as someone suggested as i don't know what driving down on a pin system, unless provisions are there to do so. Is be careful at high speeds, and not do a repeat performance. Also, purchase later, some trim gauges, as i don't have a set now with my new Smart Craft gauges, but it does accept them. I've heard several times you don't need them, you feel by the seat of your pants, where the correct trim is. And i agree to a point, still, nothing like a visual aid you have to not screw up. And as John has already eluded to, i have a fat azz, so maybe i just can't feel it as well.

Thanks again guys!

Duf

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1st Whaler hulls are not race hulls and are design for a max speed, The round bottom in the back of the whaler causes the boat to roll, This area on a race hull is flat,

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To completely discount any effects from the forces of a turning motor and prop seems to fly in the face of physics...but I am not a physics person.

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I'm interested in the problem / solution here because I'm considering a high powered temptation 25 as my next project complete with hull mods.

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James, actually i'm not new to it. I was a blow boat sailer for many years in Pensacola, raced catamarans from 16 footers, to a 19 Prindle, to a 27 ft stelletto. Tom called it similar to "broaching a sailboat" which is incorrect. Broaching is when you lose helm, and the sailboat "broaches" into the wind, putting you in irons. It is called "pitch poling" and its when the boat buries the bow, raises the stern, and you can literally toss the stern over the bow, which i have done on several occasions, on both my hobie, and my prindle. Came damn close with my 27 one time. As i have stated in several of these posts, i recognize that dropping the trim will cause it at high speed, but never understood the physics, which is why i launched this post. I also didn't know the limits when i was out testing my new 150's and erred into the bad zone trying to see where the boat was comfortable. Funny thing is on a sailboat you know your in trouble, just watching the bow, as it lowers into the sea. On my Whaler, there was absolutely no clue i was getting there, other then my rpm's dropping. As far as seeing any discernable drop in the bow, there was nothing, so its very discrete.

Plan on continuing with the break in, great advise from Finnegin and Tom, and think a 18 pitch prop will work, but not totally convinced a 19 pitch stainless new prop (the one's i have on there now are semi beat up) are totally out of the question. I still haven't got the boat to the "sweet spot" without wind interference, and being distracted but doing numerous things, as you would with a new system.

So, will truck on and keep reporting on progress, including getting up on plane with one motor. By the way, the run last week was with two people, me, a very dainty 230 lbs, and my first mate, 126 (or so she says) lbs, 1/2 tank, or about 70 gal's fuel.

Thanks again folks

Duf

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errr, broaching is when your foils (rudder and keel in large boats) "lose grip" on the water, often because you have heeled over too far. and/or you are experiencing a tremendous amount of weather helm (i.e. reaching with a large spinnaker up.)

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Op, never mind, I think I got your analogy there now Tom. I do see how there could be very similar forces at play. well, now anyone wondering what broaching was knows.

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Sailboats (and powerboats) can also broach in ocean conditions when they descend the front of a swell pushing the bow into the wave ahead. The buoyancy of the bow will make it want to rise and break to one side or the other. And yes, there will be some rolling going on.