Pros and cons on installing a finn on a merc.350 br 3, for faster planing out

SANAGI

SANAGI

New Member
Jan 23, 2013
20
lake champlain
Boat Info
2013, 260 Sundancer, Raymarine e7
Engines
350 mag 300 hp, bravo III.
Bonjour, looking at improving my cruising sweet spot, is installing a finn make it better?
 
What boat is this? Do you have trim tabs and use them?
 
I installed a fin on my AB tender and it made a world of a difference. I don't have trim tabs, but have seen many applications having tabs and the fin combination. Installing the tabs was on the radar, but after installing a fin I don't see a need for tabs anymore.

Which boat are you installing it on?
 
2013, 260 S.D.350 mag br 3, yes I have the trim pad, but
when there 4 passengers it takes quite a wild before it plaines out, so i am looking at somme solutions.
 
Installation of the fin on my tender was due to the primary goal of improving the hole shot. It did exactly that and my tender planes much-much faster now. It's been many years since I ran my POed 240DA with BIII. I assume that along with trim tabs (fully down) you're utilizing the drive trim (having the drive all the way down during take off).

If you've tried all of this and still experiencing the hole shot delay, I would try going with the fin, as this is probably least expensing and most effective option.

BTW, I don't consider having 4 passengers overloading the boat. I also don't recall having the issue with my 240DA.

Hopefully, some 260DA owners can give you better pointers.
 
You said it, all the above been tried.

merci for the inpout.
 
I'd look at other things going on, first. Is the bottom clean, for example? Prop condition? Check plugs, dist cap? With that boat, and that engine, you should have no problem getting up on plane.

A fin may or may not do anything for you. IF it helps, it will be marginal at best. The reason is that a fin can only provide "X" amount of lift. If we express that in a certain amount of pounds, we can compare that to the weight of the boat. In Alex's example, the ratio is a lot lower than it is in your boat. The amount of lift the fin will provide will not change from one boat to another - so a lighter boat will experience a much more pronounced effect than a heavy boat. In fact, you might actually run into performance problems with your setup.

I would just make sure everything is in top working order and that the drive/tabs are physically trimming all the way down. If they are, that boat should be popping right up onto plane (for a cruiser, anyway) with only 4 people onboard. And, you should even be able to pull skier or tuber.

You could also check the orientation of the celery stick (google that with "mercruiser") and change that - that doesn't cost anything... plus, you're not left with holes in your outdrive if it doesn't work.
 
The prop is nice and clean, antifowling paint, the trim tabs go down, maybe my expectation is too hight


Thanks for the info.
 
Have you reversed the drive trim spacer to the other position so that your outdrive trims down the additional inch or so?
I would try this before bolting on a hydrofoil.
And you are mentioning two separate issues - which are you trying to solve? Slow hole shot or lower plaining speed?
 
My responses were made based on the assumption that all of the technical vitals are up to the specs. Dennis implied a good reminder to review the basics. So my question would be, does your WOT and speed match the specs?
 
2006 260DA-350mag w/ B3-AC and Gen-4 people, full gas and water-no problem. Add 2 more people and it is tabs all of the way down to start. I always start with my drive all of the way down and start to trim it as she planes out. I cruise at 3800rpm with 1/2 trim on the gauge at 28-29mph (GPS). I plan to flip my celery stick this spring just to see what it does and if I can tell much difference.

I have played with the tabs when lightly loaded and she does pop up a little quicker, but I typically don't use them unless necessary.

Bennett
 
I have a 2007 240 SunDeck 350 Mag BrIII.... Six people on board and it jumps out of the water and on plane in no time at all.
 
We had a similar problem getting on plane. Switching the celery stick fixed it.
 
When you say celery stick what do you mean, or where is it located ?
 
I'll let the more mechanically-inclined members of the site (Dennis?) give you specifics, but there is an adjustment where the BIII trim cylinders attach, which allows you to increase the down-angle of the drive when fully lowered. The adjustment is made by disconnecting the trim cylinders and turning a spacer/bushing which resembles the cross-section of a celery stick.
 
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