Trim Tabs or Smart Tabs?

NYharleyrider · Post by **NYharleyrider** » Mon Oct 25, 2004 9:48 am

Has anyone ever thought of or tried using these.

http://www.iboats.com/mall/index.cgi?prod_id=24438

I wonder if they would benifit an X or an M

Bobby T.-26X #4767 · Post by **Bobby T.-26X #4767** » Mon Oct 25, 2004 9:49 am

fugget-a-bout-it...

richandlori · Post by **richandlori** » Mon Oct 25, 2004 9:56 am

I actually remember reading that Macgregor warns not to use these or you could risk instability. I will try to remember where I read this and post it. Any one else remember this?

Rich

Moe · Post by **Moe** » Mon Oct 25, 2004 10:22 am

Once the water pressure exceeds the actuator load rating (maximum lift) the trim plates move up to a horizontal position eliminating any drag.

Drag is proportional to lift. Whether the lift is being applied to the stern, as it is at low speeds, or whether it is being applied to raise the tabs against the spring pressure, as it is at higher speeds, these tabs are generating lift as long as the boat is moving. And as long as there's lift, there's drag.

--
Moe

Mark Prouty · Post by **Mark Prouty** » Mon Oct 25, 2004 10:31 am

Closest I could come:

Do not install a lifting hydrofoil on the cavitation plate of the outboard motor. These are airfoil shaped wings, offered in various sizes and shapes. Their purpose is to provide lift at the stern of the boat. This raises the stern and forces the bow down, allowing the boat to get up on a plane more quickly. If they do keep the boat level when coming up on a plane, the ballast tank may not drain completely when the boat is underway. You may think you have an empty tank, but you may not.

These hydrofoils create another problem when the boat turns or leans sideways while underway. The lift that they provide goes straight up the centerline of the outboard motor, adding a strong force to promote further leaning or capsize.

These devices can exert a large amount of force; enough to snap off the cavitation plate that is cast as part of the drive shaft housing. Avoid them

Bottom of page:
http://www.macgregorsailboats.com/safety.html

Incidentally, I have a a lifting hydrofoil on the cavitation plate of my outboard motor and like it.

A couple of points I thought interesting:

If you are caught in an electrical storm, dont touch anything that is metal, including the mast, shrouds, boom, lifelines, rudder, tiller or metal hardware. If possible, dont touch anything that is wet. Many experts recommend that a heavy gauge copper wire be securely fastened to one of the shrouds and allowed to hang in the water to carry off the electricity from a lightning strike.

Keep the crew weight aft, low in the boat, and centered from side to side. Keep the crew in the cockpit, sitting down. The rear of the hull is relatively flat, and the nose area has a deep V to allow the boat to slide through waves with less slamming. If there is a lot of crew weight forward, the flat part of the hull bottom, which normally provides the stability, is raised higher out of the water, and is less effective in providing sideways stability. With the crew weight forward, the nose is depressed. The deep V nose shape does not contribute much to stability. When excess weight is at the front of the boat, the less stable nose area is carrying more of the weight of the boat and crew, the boat becomes far more easily capsized. Keep weight off of the forward V berth when under way, and avoid storing heavy items under the V berth. Crew members on the foredeck or cabin top are far more likely to get bounced out of the boat than those in the cockpit or inside the cabin. Anyone on the cabin top will have a natural tendency to grab the mast or mast support wires if the boat tips. That puts a heavy load high on the mast and tends to lever the boat over. Keep the weight low. Obviously, it is best to have the crew positioned so the boat sits or rides level rather than leaning to one side or the other.

Dimitri-2000X-Tampa · Mon Oct 25, 2004 10:36 am

Incidentally, I have a a lifting hydrofoil on the cavitation plate of my outboard motor and like it.

I recently removed mine (which came with my used boat) and I'm pretty sure that I picked up about 0.5 mph of speed, probably due to less drag underwater.

Moe · Post by **Moe** » Mon Oct 25, 2004 10:51 am

If you're going to use a motor hydrofoil mounted on the motor anti-ventilation plate, it becomes even more important to mount the motor up where the plate is at or above the bottom of the transom, if you don't do this, the plate will be submerged at higher speeds, with the following problems:

1. Greater increase in drag. There's some drag, even with the plate up with the water hitting the bottom of it. But submerged, there's much more.

2. Much more excessive bow lift when trimmed too far up past optimum. At higher speeds, this can cause porpoising.

3. Much more excessive bow down force when trimmed too far down past optimum. At higher speeds, this can cause "bow steering," which is the bow deflecting hard one way or another, often suddenly, and sometimes causing passengers to fall... and with an unballasted Mac, possibly roll the boat.

--
Moe

Paul S · Post by **Paul S** » Mon Oct 25, 2004 10:58 am

Not sure how well it will work on a Mac. I installed one of those stingray fins on my OD on our powerboat (185 hp) and it made everything so much better - up on plane faster. Plane at a lower speed. far less bouncy ride. Gas mileage was better by a hair. Handled better. No negative issues at all.

Not sure if I would try it on the mac. I think the stress would be on the motor/mount rather than the boat itself. I think it would help getting it on plane and making a smoother ride.

Trimtabs would be interesting to install...with the dual rudders, etc. If it would work, might be overkill.

Paul

Mark Prouty · Post by **Mark Prouty** » Mon Oct 25, 2004 11:12 am

Moe wrote:If you're going to use a motor hydrofoil mounted on the motor anti-ventilation plate, it becomes even more important to mount the motor up where the plate is at or above the bottom of the transom, if you don't do this, the plate will be submerged at higher speeds, with the following problems:

1. Greater increase in drag. There's some drag, even with the plate up with the water hitting the bottom of it. But submerged, there's much more.

2. Much more excessive bow lift when trimmed too far up past optimum. At higher speeds, this can cause porpoising.

3. Much more excessive bow down force when trimmed too far down past optimum. At higher speeds, this can cause "bow steering," which is the bow deflecting hard one way or another, often suddenly, and sometimes causing passengers to fall... and with an unballasted Mac, possibly roll the boat.

--
Moe

Thanks for your thoughts. I'll have to have a look at this.

Jack O'Brien · Post by **Jack O'Brien** » Mon Oct 25, 2004 11:32 am

The automatic trim tabs would not be good for slow speed i.e. sailing. As they could not be raised at slow speed, they would produce only drag.

At least a year or so ago I questioned if anybody had tried regular (hydraulically adjustable) trim tabs and the "Flat Earthers" all laughed.

Since many power boats effectively use trim tabs I thought the Mac - when pretending to be a 50 HP "planing" power boat - might benefit from them also. I still think they would help, especially for those who cannot tilt their motor down far enough to lower the bow. I run my Suzuki 50 DF tilted fully down (no more stop pin adjustment available) for maximum speed (I've tried less tilt) and think trim tabs would help it "plane" more than at present.

It would be good to hear of such a trial from somebody (richer and more agreeable to drilling holes in their hull than me) if trim tabs help.

Pouw Geuzebroek · Post by **Pouw Geuzebroek** » Mon Oct 25, 2004 11:47 am

Not exactly the same subject, but since we are talking about fixing stuff to the cavitation plate of the engine. I am thinking of installing the propguard to mine. http://www.propguard.net/
More out of a savety perspective, but it also seems to add some extra speed. Has anyone got expierence with such a device.

Bobby T.-26X #4767 · Post by **Bobby T.-26X #4767** » Mon Oct 25, 2004 2:25 pm

there was a guy on this site that tried the "prop guard" last year.
didn't work for him.
he was trying to sell it for pennies on the dollar.

Dimitri-2000X-Tampa · Post by **Dimitri-2000X-Tampa** » Mon Oct 25, 2004 5:23 pm

since it doesn't look like we'll get our X wet this year.

Moe, bring your boat down to Florida.

Yes, a shameless plug, and no, I don't work for the state dept of tourism

MacGregorSailors.com

MacGregorSailors.com

Trim Tabs or Smart Tabs?

Trim Tabs or Smart Tabs?

Trim Tabs