Offsetting Excess Weight/Trouble Planing

YYZRC

With the new dinghy (700lbs) and platform extension (200lbs) and no bottom paint, my old girl really struggles to get up on plane. I’m looking for ideas (short of dropping in 8.2s) that will help. I already have the 4x4 props. 

I will give in and bottom paint the boat this winter - the water is 2 degrees warmer this year than past years and the growth is insane. 

As a starting point, I am considering larger trim tabs with the hope of extending the running surface somewhat. I will also try swapping the cucumbers on the drives to get a bit more negative trim. 

Any ideas/recommendations?

aero3113

Bigger tabs should help, how much anchor chain do you have?

YYZRC

About 70’ of chain. I also moved my inverter and lithium battery up to the bow to try to help. 

aero3113

Do you have the storage bin under the fwd birth? Load it up with heavy gear or lead bars and see if it helps.

LaRea

As @aero3113 said:  although weight is the enemy, lead billets in the bow might help.  Maybe the adjustment in running angle will offset the larger displacement. 

dalek

As an experiment, you could try taking some heavy passengers and sit them at the front of the v berth.

PickleRick

The bandaid hack they used to get my 5 ton 225 hp boat on plane was chain in the bow....all chain.  At anchor with no one on the boat I'm bow heavy despite having 1200 lbs in just a motor.  

Like the Dr who nemesis mentions, put a few passengers in your bow. 


And since it's not my money some high output 502 motors and new XR B3 drives sound like the ticket lol. 

Liberty44140

Before changing tabs go the easy way and buy Bennett’s drop fin kit. $45 for all 4 fins you need and they make a big difference in getting more out of your current tabs. Should work on Lenco

Liberty44140

Actually they have come down in price since I bought them:

https://defender.com/en_us/bennett-drop-fin-set-df12

will give you the performance of tabs 6” wider than the tabs you put them on

tricountytrail

Im also trying to bring down my bow I can do it but have to run my 496 mags with bravo 3 to about 3800 rpm. If I reduce rpms the boat will come of plane. I have the inserts in the position the keeps the drive more bow down. I was also thinking larger tabs, but will look into Bennett’s drop fin kit.

YYZRC

Liberty44140 said:

Before changing tabs go the easy way and buy Bennett’s drop fin kit. $45 for all 4 fins you need and they make a big difference in getting more out of your current tabs. Should work on Lenco

Did you have them on your 342? I read some negative comments about them causing the boat to be very twitchy due to bow steer. 

My Lenco tabs have creases on either side that would prevent me from cleanly installing the drop fins. 

tricountytrail

I have the same and was going to install then inboard on the flat tab parallel to water flow flow.

Liberty44140

I did not have them on the 342, just my current boat 

YYZRC

I am going to go for a swim next weekend and see if I can get a 18” wide tab on there without being too close to the outdrive. 

tricountytrail

What size tabs do you currently have?

YYZRC said:

I am going to go for a swim next weekend and see if I can get a 18” wide tab on there without being too close to the outdrive. 

YYZRC

18w x 12 chord. You?

tricountytrail

I have to measure they are what came on the boat factory. 
Thinking of adding 

Bennett Drop Fin Set - DF12 added to current tabs

YYZRC

They look 18x12 to me. 

rasbury

So, how big is the admiral? Just kiddin...my 270 leans at dock but I easily level it with the lencos...

tricountytrail

Let me know if you find a Lenco tab I didn't find anything with a longer than 12" chord.

tricountytrail said:

What size tabs do you currently have?

YYZRC said:

I am going to go for a swim next weekend and see if I can get a 18” wide tab on there without being too close to the outdrive. 

YYZRC

I’m going to bolt a larger plate to my existing tabs. Will probably do around 15x21 and may incorporate a drop fin style edge. TBD on that. 

tricountytrail

Please let me know the results and some pics because I'm in "The same BOAT"

YYZRC said:

I’m going to bolt a larger plate to my existing tabs. Will probably do around 15x21 and may incorporate a drop fin style edge. TBD on that. 

YYZRC

@LaRea I need your engineer brain for a moment, please. 

Deadrise at transom is 18 degrees and the existing trim tab is rectangular. Let’s assume that the tab fully deployed is at a 30 degree angle from perpendicular to the transom, meaning that the factory tab with drop fins installed would have the fins at a 6 degree angle out of parallel (1/3 of 18 degrees) with the hull when fully deployed. 

To account for this, I’m considering a parallelogram shape for my tab plates with a 3” drop on either side (same shape as the Bennet drop fins). This should be optimal at launch and would push water outwards slightly when the tabs are partially deployed or stowed. My concern is when one tab is deployed more than the other and the flow imbalance; but the same issue exists with the Bennett drop fins. 

Thoughts? Here’s a sketch of the proposed starboard tab. 

Note: I will measure the actual trim tab deflection when fully deployed and adjust the math accordingly. 

LaRea

I think your geometry is right, but I haven't seen parallelogram tabs before.  I'm guessing that if the drop fins are not parallel to the water flow, the side force puts tension on the hinge fasteners.  

You're adding 50% more tab area, plus drop fins.  You'll need at least 50% more force from the actuators.  Are they strong enough?

Can you first try it without the drop fins, and see if it solves the problem?  Only add the drop fins if you need them?  

YYZRC

I assume that most trim tabs on mass produced boats are rectangular for cost/compatibility reasons and not because they are optimal for a given hull design, but I am certainly not educated in this field!

The Bennett drop fins would only be parallel to the hull when the tabs are fully retracted. My proposed approach would have the drop fins only parallel to the hull when the tabs are fully deployed (and arguably when preventing the water from spilling over the tab is most important).

I read a number of great posts by a guy who went by “Tabman” on several forums. He worked for Bennett and made recommendations to improve tab performance. His recommendations were always bigger tabs first and then drop fins second. All the tab sizing charts recommend 36” x 9” or 36” x 12” tabs for a 35’+ boat. Double what Rinker installed. 

My proposed approach is a one piece tab with the drop fins bent (not bolt on) so I only get one shot at it. To your point about increased surface area, I may need to go to a dual actuator setup

I appreciate your thoughts. 

oscar1

My two cents, Why you don't look for the Lenco single or double actuator Extreme Duty design or the high performance one. Plus take a second look at your dinghy david to see where you can lose some weight. 

LaRea

When they say 36x12, I think they mean the total length is 36.  So two 18x12 tabs would meet their spec.  But with all the weight you've added at the stern, you need more than the typical recommendation.

I've seen posts by Tabman -- seems to know his stuff.  

YYZRC

The size guidelines are per side for sure. 

YYZRC

oscar1 said:

My two cents, Why you don't look for the Lenco single or double actuator Extreme Duty design or the high performance one. Plus take a second look at your dinghy david to see where you can lose some weight. 

I will look into the other Lenco options. There isn’t really any opportunity to reduce weight conveniently but I am looking for things that I can move forward (rather than just adding ballast). 

I will move the spacers this weekend and will report back after that is done. Maybe I can get away with just the spacer swap and slightly larger tabs.

LaRea

A 2007 370 is 40 feet long, but it would be impossible to fit 40" tabs on each side.  It would be hitting the outdrive.  It can hold 18", maybe 24" if you go across the strake.

YYZRC

Many inboard setups have dual trim tabs on each side of the v. Another downside to big boats with sterndrives I suppose.