Trawler trim tabs

[Greg QS]

Afternoon all.
I have a 61' Nordlund raised pilot house. I pushed up the throttles for burning out the turbos . Pushing 20k. at 70,000 lbs. Seemed to be pushing / bow high. Anyone use trim tabs? I do not plan on pushing that hard, however when needed is nice to have the ability to go.

 

[rslifkin]

My boat has them and they're basically required for it to plane decently. Just not enough lift aft without them so it runs very bow high and doesn't plane cleanly unless there's some tab deployed.

They're somewhat useful at lower speeds as well, as in certain sea states deploying a little bit of tab improves the ride even below hull speed.

 

[Greg QS]

What type of tab. Paddle type or blade typs?

 

[rslifkin]

What type of tab. Paddle type or blade typs?

Mine are the standard Bennett tabs, not the modern interceptor type. Mine are 48x12, which is significantly larger than recommended for a 38 foot boat, but the extra surface area needs less deployment angle and is generally more efficient (less drag for a given amount of lift with the wider span tabs). The majority of the components are original to the boat (38 years old) and still work fine.

The interceptor type tends to be less suitable on slower boats from what I know.

 

[sjisailor]

Agreed. For our 41' trawler, I was told by the boat builder that the Zipwake interceptor wouldn't do much until 15 kts or so. Seems that they rely on how the water produces lift from the turbulence in front of he blade and that needs significant speed to generate the energy.

Also agreed from previous boat that larger tabs are preferable! Side fins can help, too.

 

[Keysdisease]

What is said above referencing the difference between traditional tabs and interceptors is correct. Hydrodynamically at lower speeds tabs just work better.
What rslifkin said per sizing is also correct. Slower boats need bigger tabs, its hydrodynamics. Water flow over the tab (or interceptor) surface is what creates lift. Faster speed, more water, less tab. Slower speed: opposite.
Difference between a jet fighter wing, or a glider wing: lift
On my olde MSI with 200HP and 34ft of stuff in what's basically a Downeast hull, without tabs it will only wallow onto plane when light on fuel and "stuff." Without tabs and a standard load it pushes a bunch of water with the bow very high.
With the 42 x 12 Bennett tabs she wallows onto plane much faster, and stays on plane at a slower speed, even with a full load.
The larger tabs also allow for some port/starboard trim at displacement speeds which is convenient with wind on the beam or load imbalance.

​

 

[luna]

The standard 54” x 12” Bennett trim tabs on my 57’ Tolly (66,0000# dry) is just enough to make a difference at about 17 knots. They bring the bow down a bit and I gain about half a knot.

At any speed below that, it’s really hard to perceive any effect. Perhaps they are on the small size.

I do not need them to plane as with 1600 hp on tap, I top out at about 25 knots.

I rebuilt the rams 2 years ago and replaced the planes in their 28th year, this year. They seem to work fine although they are slow, in that it takes about 20 seconds to do a full stroke of the rams.

They must be an important system as I have put about $2000 into them in the last few years.

 

[rslifkin]

The standard 54” x 12” Bennett trim tabs on my 57’ Tolly (66,0000# dry) is just enough to make a difference at about 17 knots. They bring the bow down a bit and I gain about half a knot.

At any speed below that, it’s really hard to perceive any effect. Perhaps they are on the small size.

I do not need them to plane as with 1600 hp on tap, I top out at about 25 knots.

I rebuilt the rams 2 years ago and replaced the planes in their 28th year, this year. They seem to work fine although they are slow, in that it takes about 20 seconds to do a full stroke of the rams.

They must be an important system as I have put about $2000 into them in the last few years.

It's entirely possible your hull design just doesn't rely heavily on the tabs for lift to plane and only uses them for trim adjustment. This is more likely to happen with boats that carry chine flats all the way aft and have other design aspects to add lift. Other hulls end up with plenty of lift forward, but are short on lift aft and need the tabs more. Mine is like that, as the chine flats twist out entirely about 1/3 forward from the transom and the boat narrows a little towards the stern as well, so there's just not enough lift until the tabs are deployed a bit.

 

[Greg QS]

The standard 54” x 12” Bennett trim tabs on my 57’ Tolly (66,0000# dry) is just enough to make a difference at about 17 knots. They bring the bow down a bit and I gain about half a knot.

At any speed below that, it’s really hard to perceive any effect. Perhaps they are on the small size.

I do not need them to plane as with 1600 hp on tap, I top out at about 25 knots.

I rebuilt the rams 2 years ago and replaced the planes in their 28th year, this year. They seem to work fine although they are slow, in that it takes about 20 seconds to do a full stroke of the rams.

They must be an important system as I have put about $2000 into them in the last few years.

Is this a Ed Monk desighn. Nordlund yachts (mine) made a lot of hulls for tolly back in the day. You may have the same hull style as mine. Do you have any bottom shots? . Im 61' at 70K lbs .

 

[Endeavor GB 32]

Some people think that "trim tabs" and "trawler" don't belong in the same sentence without "do not belong on" between them.
Regards,
Scott

 

[rslifkin]

Some people think that "trim tabs" and "trawler" don't belong in the same sentence without "do not belong on" between them.
Regards,
Scott

In my mind it has nothing to do with what the boat is, etc. It's all down to "do they provide any operational benefit on this specific boat?"

 

[luna]

It is said to be an Ed Monk Jr. design, which is called for marketing reason a Quadra Lift Hull, (whatever that means) and was promoted as being built under the Rules of Certification of ABS.
Although nowhere can I find if it was actually certified.

The hull is 57' x 17.25' but if you add the bow and stern platforms the boat drives at 62.5' long.

It could be that your hull shares some of the same qualities as mine but I think you may be more similar to the 61' or 65' Tollys.

Sorry I don't have any bottom shots that would help.

You certainly have a nice boat.