87 340DA Stern heavy

T

TWINSCREWED

New Member
Mar 15, 2011
6
Great South Bay LI, NY
Boat Info
340 DA 1987
Engines
Volvo 8.1l
Hey Tabman, I have a question. I have an '87 340 Sundancer and under stock configuration it tends to be a stern heavy vessel. When I add my inflatable to the swim platform or have a couple people on the transom seating the boat just doesn't want to push the bow down unless i'm running the boat really hard (3600 rpm +). My boat does have an Isenglass extension vertical from the windshield 12" which connects to the raised bimini top. I have noticed that the above listed condition is lessened when that isenglass is removed. This condition has really made me hessitate on adding on extended swim platform that I would love to do. The boat currently has the stock configuration of 26" wide by 12" long tabs with single pistons. I was thinking about going to twin pistons/hpus with an extended tab, as there is no room to add width. My thought was to go to at least 16" long but considering 18". Do you have any recommendations? :huh:
 
Twin,
Do you have a photo of your boat's transom? I'd like to take a look fist. Adding surface area is the way to go and it's a good idea to ad an actuator to each Trim Tab. 18" is pretty large even with two actuators, there will be a lot of leverage on them when you back down.

Let me know if you have a picture and we can take it from there.

Tom
Bennett Marine
 
My 87 340DA looks just like your 87. Years ago the Tabman
sold me wider and longer tabs with a little turn down on the outside edge. Still single actuator. They work great and I
carry about 50% tabs once I get on plane with 3200 RPM.

Dinghy and motor on the step but not extended swim step.
 
Twin,

Happy Hour is on the right track. The first thing I would recommend is to install 30" x 12" Trim Tabs with what we call "dropfins", it looks like you have the space:
srdf.jpg


Drop fins are 3" extensions that capture water pressure that normally escapes out the sides of the Trim Tabs and channels it aft to generate additional lift;
MP80820587.jpg



This would hive the maximum lift with a 12" chord Trim Tab.

If you feel that you need more lift after that you could extend them but I would recommend staying closer to 16" even if you put dual actuators on them. The 30 x 12 will be fine with a single actuator.

If you do extend them you should incorporate the drop fins in the extension for best results.

Tom
Bennett Marine
 
Happy Hour thanks for the response. My wasn't too bad before the repower, I have 8.1's installed a couple years ago and I think the installation has made the condition worse. Although the engines still sit in the same place, alot of the ancillaries got moved around, most notably the exhaust is located in the back like the newer boats. Do you run the four blades? that gave me 2.5 knots at cruise by themselves (before repower). The boat does outstanding when not carrying the inflatable, but really tends to drag with it.
Tabman takes for your response as well. My only concern with going wider with the drop fins is that when I spoke to searay they said that I should retain a step back off the tunnels or at a minimum I should taper the inboard edge of the tabs outward aft at twice the angle of the tunnel intersection with the transom. Their reason was that the pressure on the inboard edge of the tab from the prop wash would distort the tab and could cause damage to the hinge and tab itself. Is that a concern? It seems as though all the pocket drive style hulls I have seen seem to have that step back or the tab inboard edge relieved outboard. My thought was that I could extend the tab to the pocket and taper it back and pick up the approx 12 sq in with a majority of that near the transom or possibly use the drop wings near the width as current or use the drop wings only on the outboard side and relieve the in board as suggested by Sea Ray. Whew. if any of all that seems tomake any sense at all. :smt101
 
Twin,

I don't think you have to worry at all about the prop wash damaging the Trim Tabs. Trim Tabs have been mounted right next to and over propellers on "conventional" transoms for years without problems. I have helped with and seen many installations with the Trim Tab right next to the propeller pocket and all have worked well.

These two photos are of an extension an owner added to a set of standard 12" Trim Tabs with Dropfins. Note the proximity to the prop tunnel.
9bc5kg.jpg


30w6lvk.jpg


Here is a boat with four Trim Tabs, again note how close they are to the tunnels.
l_317-1.jpg


Here are four Trim Tabs mounted in a "conventional" transom, the inner Trim Tabs are actually overlapping the propellers, so they will certainly be in their wash.
P1010148.jpg


All of these installations work very well with no problems.

I think the guys at SeeRay may have "lost the history" of the Trim Tabs with the angles cut on the inboard sides. They were originally for boats with inboard outboard drives. The reason for the angles was to prevent disturbing the waterflow to the propeller on the outdrive since it is aft of the Trim Tab. Without the angle the Trim Tab could cause the propeller to ventilate.

On side benefit of the dropfin is that the 90 degree bend in the metal adds considerable stiffness and prevents it from bending.

So, long story short, my experience is that mounting the Trim Tabs right up to the tunnel works just fine.

Tom
Bennett Marine
 
Last edited:
Twin, just like Tabman says. My tabs go from the edge of the tunnel to the chine at the outside. They cannot physically be any larger without hanging in the air.

I suspect most of the benefit I received is from the fore-aft length increase of the tab, but that is just gut feel. The extra width didn't cost anymore and sure didn't hurt.

I am running the 4 Blades. As a side note.. before I got the larger tabs I decided to put her on a diet. I took 200' chain out of the locker thinking it would improve performance. Took forever to plane and I had to carry another 700 RPM to keep it there. Bad idea so the chain went back in.

After I got the larger tabs I tried removing chain again. Again a little slow to plane but once it got there I only needed about 150 RPM and more tabs to stay there. So the chain is back in. This did show the advantage of the tabs 700 RPM - 150 RPM.
 
Tabman, thanks for the fast reply. Unfortunately work keeps interupting my boat related activities. Nice to get input from someone who has actually done it and not just heard about it. You have really addressed all my concerns and helped to make up my mind as to which way to go. Looks like the best approach for me is to go wider to the tunnel and alittle longer with the drop fins. With this boat, I don't think going to far could ever be a problem and will help with the additional weight added to the transom with the extended swim platform. It really amazes me how bad the balance on these boats is to start with. A good friend of mine has the express version and it runs and handles like a completely different boat but unfortunately does have the requisite berthing areas for me. I already have a set of actuators and an additional HPU from a previous boat that had met its untimely demise, so adding that isn't a problem. Honestly, the quality and life span of the Bennett product line is awesome and seems to never be a problem. I had already added the RM12 which really help with the line loss in the wire runs, which was a big improvement. I just have to hope that I can get this accomplished prior to being kicked out of the boatyard, as i was a last haul out for the winter.
Happy Hour: Totally get the idea of putting her on a diet, although I went the other way. I actually added a water bladder under the forward berth. I had thought about going to all chain but opted for the water bladder instead. The only problem is to make sure the bladder is drained prior to the winter,not sure that would be a problem for you in California. I run about 30-40 gallons in there which helps for those long weekends and a family that isn't water conscious at all. I plumbed that under the floor to a Jabsco water puppy to transfer the water into the main tank under the dinette. Does your boat have the canvas going straight to the windshield, like the factory set-up or do you have the rise of eisenglass up to the bimini? I find a pretty large difference in running with the eisenglass up and down.
 
I am in the process of adding additional trim tabs to my 1997 400DA. I am very interested in the modification to the trim tabs. Are the tabs with drop fins a local mod or for sale from Bennett?
 
Depending on the size, dropfin Trim Tabs are available from Bennett, usually thru a dealer. Do you know what size you can fit?

Tom
Bennett Marine
 
i have a 1985 34' sea ray sun dancer with the same problem. I can't get my bow down. Are these upgrades available to purchase as a stock item ?
 
Why Go Home,

I would need to know what space you have on the transom for larger Trim Tabs with drop fins.

Do you have a photo of the transom and perhaps measurements?

Tom
Bennett Marine
 
I don't have a photo, the boat is in the water, but it is the same exact hull as 87 340DA Stern heavy. This will be a winter project, trying to get all my info together. I will try to get a photo of my actual hull when I haul. Any insight until then?
 
Tabman, thanks for all the info you've posted. I too have a late 80s (1989) 340 Sundancer. My dancer has all chain rode and I agree, that does seem to help (I sea trailed a few 340s before purchasing this one). I like the idea of the water blatter and I will probably go that route as well. My boat has factory 30" x 9" tabs and I cruise with them all the way down. As soon as I let up on the tabs, I start losing mph.

Thing is I ALSO want to add an aftermarket swim platform and I'm concerned about the additional weight when planning. If the 30" x 12" works at 50% for Happy Hour without an extended swim platform, how do you think they will work with an extended platform carrying a dinghy? Bigger? Of course the all chain rode and additional water in the bow will help offset the additional weight of the extended swim platform. BTW, the spot under the master berth is perfect additional water storage, it's huge and not at all easy to get to.
8-13-2012 006.jpg

Thanks in advance!
Rob
 
Rob,

Replacing the factory 30 x 9 Trim Tabs with 30 x 12 with the drop fins will add quite a bit of additional lift and will help a lot. I think that you are on target with the additional forward weight offsetting the weight and leverage of the extended platform since even though Happy Hour doesn't have the extended platform he is carrying a dinghy on the step.

One note about additional weight forward; you want to make sure that at lower speeds the boat is not ridding in a bow down attitude as this can lead to steering issues in a significant following sea such as coming in an inlet. You may want to consider running the boat with the larger Trim Tabs and all chain rode before adding the water bladder.

Tom
Bennett Marine
 
Tabman said:
Rob,

Replacing the factory 30 x 9 Trim Tabs with 30 x 12 with the drop fins will add quite a bit of additional lift and will help a lot. I think that you are on target with the additional forward weight offsetting the weight and leverage of the extended platform since even though Happy Hour doesn't have the extended platform he is carrying a dinghy on the step.

One note about additional weight forward; you want to make sure that at lower speeds the boat is not ridding in a bow down attitude as this can lead to steering issues in a significant following sea such as coming in an inlet. You may want to consider running the boat with the larger Trim Tabs and all chain rode before adding the water bladder.

Tom
Bennett Marine
Click to expand...
Tabman, thanks for the quick reply! Good point, but I don't think there's much chance of running bow down. These boats are so aft heavy and then with the extended swim platform/dinghy, it would take a lot of bow weight to balance out. I will watch this closely to make sure I don't get into this situation even though I boat mostly in the inland california delta and we don't get a strong following seas. However, since I will occasionally make the trip out under the Golden Gate, I wouldn't want this issue.

It seems West Marine doesn't sell the tabs with the drop fins? Suggestions for a north CA vendor?

Thanks again,
Rob
 
Rob,

West will special order them for you. as will any other good dealer. I don't know of anyone who will have them in sock. The part number would be TPO3012DF. This is just the Trim Plane and you would reuse the hinge plates. You need two each. If you want to rplace the hing plates too then use part number TPA3012DF, that is the Trim Planes and the Hinge plates, again you need two each.

Tom
 
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