Lenco Trim Tab Upgrade (Again?)

[grouperjim]

Mark:

At 6/7 you can see that the flotation bracket is clearly completely out of the water. The tabs are much lower than the lowest part of the bracket so I can rule out any part of the bracket touching the water while on plane.

I have NO protrusions from the hull of my boat other than the factory bronze raw water scoop on the port side which will account for some of the variation between prt and stbd turbulence as well as the RH spinning prop. Starting at 28/29 you can see four lines of turbulence come into view. The most outboard is the hard chine, then the outside edge of the blade, then the strake, then a combo of the scoop/inside edge of the blade near the A/V plate.

I did note above that it is 16" to centerline (might be just a hair less to the plug) but I'll take a more precise measurement to the drain plug tomorrow.

jim

 

[Megabyte]

I haven't made contact with Tom McGow yet...I sure hope he looks at this.

I just dropped Tom a note.

 

[grouperjim]

OK. I've accounted for each stream of turbulence in the video. In the center of the tab swath is the slight turbulence from the strakes which roughly bisect each tab. On the port side is the addl turbulence (even closer to prop) from the scoop.

BTW the reason for converging vortices is that the majority of lift from the tab is from the force of the water spilling out the sides of the blade. That is why wider tabs are more effective than longer ones with comparable surface area. The newer 25MVs have a recessed tab with bat wings that bend downward on the sides to contain the spillage and increase lift on the back edge.

Again, my boat is performing flawlessly in this configuration. I only pointed out the "converging vortices" so you can plan/fabricate accordingly. I believe your hull has a wider beam, so the 30w are fine as many other CPers have those with no issues.

If you have a ventilation issue, try a Permatrim......they really work especially on a Parker with an Armstrong bracket. Lower your engine on the holes until you resolve the issue. Regardless......plenty of info here to pull the trigger on the tabs! Good luck.

jim

 

[DaleH]

No offense intended Mark (Chop Chop) but could your vent problem be how you run the boat? Meaning, and I find this too on my Parker, she is pretty sensitive to trim angle and OB trim position.

When up on plane, with tabs deployed to the sea state and best fuel mpg, I'll trim the motor out 'til she ventilates and then trim down to prevent it. But, if I need to make a MAJOR heading correction, say > 15-degrees of my initial heading, I'll need to trim the motor down a bit to allow her to 'dig in' and stay hooked while in the turn.

I find this to be the case on my boat due to the almost 10' wide beam AND modified V hull. Turning the boat really lifts the motor higher in the water column.

I also don't think you'll have an issue with those 30" tabs as you're planning on mounting them.

 

[Megabyte]

if I need to make a MAJOR heading correction, say > 15-degrees of my initial heading, I'll need to trim the motor down a bit to allow her to 'dig in' and stay hooked while in the turn.

Same with my boat. (1996 MVSC, 14 degrees deadrise)

When coming into my creek, I have 2 aton's I need to 'slalom' around to follow, and stay in the channel.
Both turns require a 90 degree change in course.

If I'm not trimmed in, or if I don't slow down considerably, I'll ventilate every time.

 

[Chop~Chop]

Thanks Again Jim, You're right I should have enough info. here to pull the trigger...literaly on the drill... :?: :roll:

My apologies, I didn't notice the data you previously provided; I was too amp'd up watching the video.

If I end out mounting my 30x9 tab like yours, I will end out with essentially the same 16" clearance to the cenerline as you have with the 24x12 tab and I should be fine...But, in this case, the actuator will be too far outboard to allow routing the hydraulic line, have access for maintenence, and be able to properly fasten the fitting.

Since I'm planning to just go half way with the install; use the lenco actuators for this year. I am still considering whether or not the hole I would drill in the center of the upper actuator hinge for the wire will eventually be useable for a hydraulic line. If not, I'll probably drill the hole above the hinge as if it would otherwise be the hydraulic line.

Sorry to belabor this; but your description of the convergence of the vortices caused by spillage out the side of the tab and the downward bend in a tab to contain it, makes me consider the following:
I'll have adequate access for the hydraulics if my estimate of a 4" shift inboard is correct.
Since a 9" chord will create less turbulence than a 12" one, I could concievably mount closer to centerline and should not have a problem?

And, I like the idea of fabricating a bat wing on the inboard edge of the tab. I think a professional metal fabricator could do this easily; add a 90 bend to inboard edge.

I'd appreciate your inputs but I sure hope I/we get professional help...Else I ain't launching until after the 4th of July.

-Mark


Dale, not a probelm...I think I know what's up with that...
How'd you get hydraulics routed, from the upper hinge, directly through the transom??

 

[Megabyte]

I like the idea of fabricating a bat wing on the inboard edge of the tab. I think a professional metal fabricator could do this easily; add a 90 bend to inboard edge.

'Bat wings' are available from Bennett as an option, and can be bolted to any of their tabs.

PM GW204 as he installed a set on his previous boat. I think he may have even documented the job here in the Projects area.

 

[grouperjim]

The cool thing about Classic Parker is that you can take all the risk/surprises out of doing a project because someone here has done it before.

It would be tough for me to surmise what the exact effects would be on your hull. My deadrise is different and beam narrower. My best advice would be to duplicate the install of another 25MV owner for guaranteed results.

jim

 

[Chop~Chop]

I think I know the risks thanks to all of you. If I end out going with indoor plumbing as planned then I won't be surprised if I have to go with a bat wing approach or 24x plane to get it right...

Unless of course, if I figure a way to install as Dale did, I could likely have this rig rigged ok from the get-go.

For now, I'm thinking the advantages of indoor plumbing and more lift outweigh the risk of using 4" less clearance with my 30x9" trim planes.

Thanks Again, Mark

 

[Chop~Chop]

Here's an update. No adverse effects of mounting the 30x9 tabs 12 from centerline. The white-water on top of the anit-ventilation plate is a little disconcerting. But,I think it was always that way... The performance is unbelievable. With the tabs deployed slightly I can actually now trim up the motor above 3 bars without cavitation. I actually replicated Dale's and Kevin issue when running the slalomn course with trim up 4 bars...

Yesterday I had her out in 2ft. chop and she now lives up to her namesake. The boat actually just feels heavier with the bow towards the horizon rather than the sky. Very comfortable ride at 20kts turning 4000 rpm.

Not sure yet what to make of this test of the first full day out a week ago...FAC conditions, tabs full retracted, trim down all the way. Throttle postion set to run at 3500 rpm she gets to 13 kts. Next, deploy tabs ~30% and simultaneously trim up 2 bars...wait...she gets to 19kts turning 3900 rpm. Next retract tabs and trim down... back to plowing at 3500 rpm.
Seems like increased efficiency is only less by the the addition fuel burn of turning 3900 vs 3500 of the nearly 50% increase in speed, 13 to 19kts...All attained by just touching the buttons!

Obviously, I still only spin 5400 rpm at WOT; seems l like the REV4 14 5/8 x 15" might be the ticket? I'm not sure how to judge if the motor should be raised a notch or two? I'm currently mounted on the top hole, i.e., motor is all the way down.

Thanks, Mark