Trim by Wake

[JLR]

I have been boating for a long, long time. When trimming my boats, I have always found that the flattest wake directly behind the boat gave me the most speed. You remember what a nice flat outboard wake looks like. I finally ditched the Bennett Auto Tab Controller on the Ocean (another story for another day) and have been tinkering with my trim tabs manually to adjust them for the maximum speed on the Ocean. For the first time ever in all my years of boating, on this boat, the flattest wake aft of the boat does not offer me the greatest speed. I do not know why, but using the tabs to create a bit of a rooster tail offers me about one knot more speed than when the wake is at its flattest. Any thoughts on why?

 

[Avenger]

If I overtrim my boat it looses speed too. Putting the bow too far down increases wetted surface and drag.

 

[drburke]

From reading the Jack Hargrave biography book, I know part of his design philosophy (and sport fishers in general) is to run slightly bow up around 6 degrees to aid in over-riding big waves and present as much of the deep vee hull to oncoming water as possible (technically modified deep vee).

So in Derek’s case I am not surprised that is designed to be point of lowest drag. But odd to find on MY style, I agree.

DAN

 

[Avenger]

That seems pretty reasonable. I know on my boat speed and load is a factor. Below my normal cruise more tab will usually increase speed. Beyond that it gradually develops a detrimental effect and at max it definitely slows the boat down. And I could see a MY being designed for a different cruise trim because of it's application, and it probably has a more forward weight distribution. JLR is talking about his Flexible Flyer, not the MY.

 

[Cricket]

John, all of the newer fast boats seem to throw a rooster tail instead of a flat wake, must have something to do with the increased speed. Might also be related to strakes as most newer hulls have them.

 

[carolinacoast]

Avenger is correct. Reducing wetted surface increases speed. Wake is an effect, but not causal.
The America's cup foiling sailboats are the most extreme innovation to reduce wetted surface.

 

[Pascal]

I always trim by the gps number and hav never paid much attnetion to the wake. Havent done much testing on my recently repowered 53 but the new 54" trim tabs did get her on plane

Most boats require full trim tabs to get up quickly but as speed increase it usually pays to decrease trim tabs as drag goes up

Some boats dont need and dont have trim tabs yet just hop on plane with minimal bow rise. Lazzara for instance didnt use trim tabs on some of their boats like the 80 and 84 but instead used a thin strip on stainless steel, about 1/4" where the tabs would be. This gives enough lift to eliminate bow rise (i measured on 3 degrees getting on plane) and yet appears to have minimal drag

 

[JLR]

Thanks all. Although the wake looks best when the bow is almost all the way down, the GPS numbers say I need to trim it up a few degrees to gain speed. Pretty unusual, at least in my experience, but I will take the speed anyway. Also, for what it is worth, there is no difference in the load factor whether the bow is down or up a bit.

 

[krush]

Pretty unusual, at least in my experience, but I will take the speed anyway.

Every boat I've run goes slower with the bow dug in by using too much tab (or on I/O or outboards, not trimming up the drive). This is true on my hatt as well. If the boat has enough power and stern lift, no tabs will usually be the fastest at high cruise. Note: I've never run a MY that doesn't plane.

 

[Boatsb]

I believe the wake is also effected by the props.

When I played gofast a change in prop shape would change lift and require different trim and jack positions.

 

[doc g]

I think the other issue at hand is the fact that Hatteras went intentionally smaller with the trim tabs on the MY's especially the bigger MY's so much so that it is impossible to over trim the bow too low. I guess for safety. Most other boats I've run (besides my Hatteras's) I could over trim the bow down and lose speed especially at cruise RPM and as someone else said at WOT fastest speed was with no tab. I think the Ocean just has more trim available than your Hatteras's had in the past...... ......Pat

 

[SKYCHENEY]

I always trim by the gps number and hav never paid much attnetion to the wake. Havent done much testing on my recently repowered 53 but the new 54" trim tabs did get her on plane

Most boats require full trim tabs to get up quickly but as speed increase it usually pays to decrease trim tabs as drag goes up

Some boats dont need and dont have trim tabs yet just hop on plane with minimal bow rise. Lazzara for instance didnt use trim tabs on some of their boats like the 80 and 84 but instead used a thin strip on stainless steel, about 1/4" where the tabs would be. This gives enough lift to eliminate bow rise (i measured on 3 degrees getting on plane) and yet appears to have minimal drag

Pascal,
I haven't seen any numbers posted on the performance after repower. I'd be curious as to what your WOT speed is with that configuration.