Trim Tabs usage

[osd9]

Just wanted to see if others have the same experience and also take the time to share my own.

With both my '93 and '98 330DA with V-Drive inboards, after I was on plane, I would apply a little trim and I would notice the RPMs and speed increase without giving any more throttle. There was the point where too much trim would cause the opposite effect so I would back off a pinch and go on my merry way...adjusting for side to side as the need arose. My reasoning was that if the engines RPMs increased and the boat went faster, that I was running her at her most efficient point.

On my '02 380DA, applying any amount of trim, would cause the RPMs and speed to decrease, so I just figured that the different hull, extra weight, etc, made the difference and I just concentrated on finding the "sweet-spot" (RPM wise)...using the Smartcraft instaneous fuel burn, GPS for speed and a helper with a calculator...Once I found the MAX Miles Per Gallon, that was my sweet spot...(Generally right around 3400 RPM would yield .85 MPG)

Now, when I drove my new 410DA (a 6 hour ride for delivery) I was suprised to find that it reacted to the trimming the same as my 330DAs did......a little tab and the RPMs and speed would increase....

So, my question is....do others (and very curious as to other 410 owners) use the same techniques to find their sweet spot for RPM and MPG? Also, are there other techniques that you could suggest?

Thanks...

 

[Dave S]

Obviously I can't answer our question since my only experience is with outdrives on much smaller boats.

But I would like to understand why trim tabs (when deployed) would actually increase your speed. On an outdrive, you trim the drive up to increase speed because that actually pushes the back of the boat down a bit which raises more of the hull out of the water when on plane and that creates less drag. With trim tabs deployed, whether it's an inboard or and outdrive, aren't you (in effect) raising the back of the boat which pushes the bow further into the water? I would think that would create more drag and slow you down.

Maybe someone a lot more knowledgeable than me could explain this. :smt017

 

[ImpulseIII]

Dominic,

Maybe I am doing this all "bas-ackwards" but...I use the tabs to get the boat on plain as quickly as I can then I set the engines at 2450RPM (if I am going any distance) and trim for max speed at that RPM. The Revs stay constant .

I have two other "sweet spots" at lower rpms and I actually like to run their when I have no place specific to go. I use the same "tab methodology" at those rpm's as well.

I keep hearing that I should run the boat at 80% of WOT at all times (obviously not in no wake zones and the like) but the boat feels so good at other, lower RPM settings, I use them often. I have one spot at 2200 and another at just under 1900 and just barely on plane.

Going back to my old "car guy" days, I do "blow the carbon out" on the way home to the marina by running at WOT for a few minutes but I am actually not sure if I am doing any good or actually hurting the engines.

Anyway, I am sure this does not answer your question but I felt a need to increase my message count on the board!!!!!! :smt043 (you get my drift) :smt101

Merry Christmas Eve to you and all the other CSR'ers :grin:

 

[Skip]

I keep my tabs all the way up (bow up). I have found them to be unnecessary to bring the 420 on plane...there is very little bow rise with the 420 hull form and Cummins power. I simply add throttle until I reach 2100 RPMs (love that glendinning synchronizer) then I use the tabs to trim the boat port and starboard. If all guests are sitting behind me on the starboard side of the cockpit then I will use a little tab to bring the starboard side up a bit. I judge port-to starboard balance by the richie compass and the wake behind the boat.
In choppy conditions, I will typically trim the bow down a bit, not enough to slop waves over the bow, but low enough such that the bow is breaking the waves a bit. This give us the most comfortable ride. This technique increases the wetted surface of the hull, which increases drag and decreases speed, but the trade off in a smoother ride is well worth it.

regards
Skip

 

[xravenx]

Dominic

My 370 DA reacts just the way you described the 330s. Kind of wierd that the 380 doesn't run that way, being that the 370 and 380 are so similar. I can't explain it, I give my boat a little more then half throttles and it gets right on plane without struggling, is the 380 the same way?........ BTW, congrats on the new boat, I'm jealous, give me two years and it will be my turn, maybe Skip will be ready to move up by then..........hint, hint

Merry Christmas everybody.

John

 

[fwebster]

The reason you've gotten so many different answers is because each hull and power configuration reacts differently in different conditions. Ideally, tabs create drag and any application of tabs, while they may improve attitude, ride, or sight line over the bow, they will slow the boat. However, many larger Sea Rays, particularly those with diesel v-drives are stern heavy so dumping a little tab in actually improves speed since they give the boat a little stern lift.

My boat is in that category.....with full tabs she runs level, but back off about 50% of the tasbs and she is still level but picks up about 1.5 kts.

 

[Alex D]

My 340 needs a good amount of tab up to about 30 mph where I can take them all out and the hull runs most efficient without tab application. I still need some tab at 26 to 28 mph to run most efficient (read highest speed without throttle input).

I ran a 410 gas (380 hp 454MAG Horizons) that's for sale at our marina and I was floored how well that hull is balanced. It planes just as quick as my 340 (which is quite tail heavy), needs less or no tabs, albeit higher rpms to run mid-20s.

 

[Dave S]

The reason you've gotten so many different answers is because each hull and power configuration reacts differently in different conditions. Ideally, tabs create drag and any application of tabs, while they may improve attitude, ride, or sight line over the bow, they will slow the boat. However, many larger Sea Rays, particularly those with diesel v-drives are stern heavy so dumping a little tab in actually improves speed since they give the boat a little stern lift.

My boat is in that category.....with full tabs she runs level, but back off about 50% of the tasbs and she is still level but picks up about 1.5 kts.

Frank...........since you've piloted so many different large Sea Rays and know how they respond to tab usage maybe you can help me understand why any tab deployment at all doesn't slow you down once the boat is up on plane. :smt017

In your description, after you have reduced deployment to 50%, if you were to fully retract yours would your boat actually go slower assumming you didn't alter the engine RPM? Quite possibly what I am missing here is that at some cruising speeds you are so close to comming off plane, that without some tab deployment, you actually will slow down. Is that a fair analogy? And if so would it be fair to say that at higher speeds or at WOT, any deployment of tabs would slow you down?

 

[lorenbennett]

I use mine the same as Skip, adjust for weight side to side, little more for sloppy seas, little less for top speed. I don;t know about other 260da's but there is a very narrow sweet spot for trimming both tabs and engine for best ride and speed. Merry Christmas to all. :smt024

 

[rondds]

not sure if i qualify to respond here, being the only DB amongst many DAs, but i get my tabs down (about six seconds worth - not sure what percent that would be) before i even hit the throttles. i find this technique prevent excess squatting in my "rear-heavy" boat. once up and running, i'll manipulate the tabs a bit, but usually dont retract them much if at all. for me, the "sweet spot" for speed and economy (if economy is possible) is 3250rpm.

 

[fwebster]

Ron,

You are not any different than the rest of us, in fact, with a DB, you are more subject to the heavy stern thing. I don't spend much time on DB's but every one of the 34, 37 and 40DB's I've been on needs a lot of tab to get the most efficient setting ......i.e. speed vs rpm setting.....

Dave,

Your questions and observations get us in to theory, again because every hull/power setting and configuration is different. Generally, to achieve the most efficient setting with tabs it is a trade off of increasing the drag with more tabs vs decreasing the hull resistance thru the water by raising the stern and reducing therefore reducing drag. With my boat, I find that full tabs gets me up on the water in a very flat attitude where I never push the power ahead of the turbo lag...just a nice slow acceleration, so I reduce engine load, soot on the transom and since the tabs hold the bow down, I can do it this way and get no bow rise. Once the boat is hooked up and settles in at cruise speed, I back out the tabs until I see the speed increase, level off then begin to decrease....then I go back the other way a little.

One boat I know pretty well is the new style 420DA.....they have a more forward COG and really don't need tabs to beefficient when they are hooked up. But every boat is different. Any time I get on a new ( to me) boat, I start with no tabs at all to see how she handles just on her own bottom.....sometimes tabs are needed to keep the bow where you can see over it, sometimes not. Sometimes they need tabs to stay efficinet, sometimes they are like mine and need only partial tab.

I suppose you are right about borderline speed conditions where the boat is just on plane.....you would likely see this more with lower torque gas engines than with diesels.....but the application or increase of tabs could slow the boat enough for it to fall off plane. But, every boat reacts differently, so there is no always, everytime answer to whether or not this will happen because the whole picture of increased drag from tabs vs. decreased hull resistance must be considered. In the case of a 450DA, they will plane at lower speeds and lower power settings with tabs in than out because of hull lift and decreased resistance.

I might add that most of my experience is with inboards and I do stern drives differently. To me, the outdrive handles the attitude trim better than tabs so I use the outdrive trim to settle the boat in then use the trim tabs to handle weight and balance port/stbd trim only.

 

[osd9]

First things First....Merry Christmas to ALL...

I agree that applying any TAB would be counter intuitive when talking about gaining efficiency. You would think that applying TAB would just be adding drag and that drag would be IN-efficient.

That's why I was so curious.......the 380 would jump on plane with no problem what so ever....with or without the TABs down....however, any TAB while on plane would decrease effeciency....

I kind of like the way the 410 seems to be more effecient by adding some TAB because it makes the ride attitude nicer for all on board, especially the admiral..( Admiral Happy = Captain Happy... :grin: ...that equation holds true with the old math AND the new math)...

I think that Frank W is correct that different hulls, with different engine configurations, and mostly the weight distribution of the "package" has the greates effect.....

Frank H......you could have gotten 3 more count by breaking that response up....you talked about Tabs, Sweet spot and WOT.... :thumbsup:


XravenX....Thanks.....However, based on past history, Skip will be two more boats into his journey by then....You'd best get your financing ready now...

 

[Skip]

Gentlemen,
I assure you, the Admiral says I am done. We love the 420. Right boat for us. I've now owned it longer than either the 260 (8 months) or the 320. (9 months)

I am of the opinion that larger boats, if you are a DIYer, become self-limiting. What I mean is that I simply have no desire to maintain any more fiberglass square footage than I already have; additionally, to go bigger means getting into the 600HP plus diesel range, with the attendant increase in fuel consumption and cost.

Merry Christmas, all!

Skip

 

[fwebster]

Skip,

Based on your description of the limits, I figure you have at least one more step up to go.........to somewhere in the 48-50' category (since they no longer make the 450DA!)

But, do not show this thread to your wife......................

 

[Alex D]

Skip,

Based on your description of the limits, I figure you have at least one more step up to go.........to somewhere in the 48-50' category (since they no longer make the 450DA!)

But, do not show this thread to your wife......................

The 48DA is my favorite of ALL Sundancers!! :thumbsup:

 

[Odyssey]

However, many larger Sea Rays, particularly those with diesel v-drives are stern heavy so dumping a little tab in actually improves speed since they give the boat a little stern lift.

My boat is in that category.....with full tabs she runs level, but back off about 50% of the tasbs and she is still level but picks up about 1.5 kts.

That's exactly what happens with my 44EB - I get the engines to 2350, then get the bow down to pick up another 1.5K

Randy

 

[PMvdb395DA]

For the more smaller Searay's that want a ''cheeper'' system there are now electric trim tabs.
Very easy to mount.

http://www.allpa.nl/pdf/katalog/062_nl.pdf

Sorry only dutch but I hope you can see it.