Trim Tab Position

W

WarrenG

New Member
Nov 29, 2011
103
Az
Boat Info
"PEARL"
500 SunDancer 2004
All Fresh Water
Engines
Cummins QSM-11 660HP
Were do you run your trim tabs when running @ around 80% or in my case 1850 RPM ( 25-26 mph ) in somewhat calm waters(lake).
My Sundancer weighs apox. 41,000 lbs wet.

WarrenG :huh:
 
Obviously a big difference between our boats, but I run the tabs all the up at cruising speed. I will use them when turning, but thats it.
 
Warren, I have a friend with the same boat as you. He never touches the tabs; claims they are not needed. I did drive his boat for a while during a long transit and, at cruising speed, I could not see any effects from adjusting the tabs.
 
Al,
I was running the boat with them up and also not using them, however I was running this past weekend with them down( and somewhat down ) and thought I was getting a more level attitude and more speed. RPM’s stayed the same. I was lighter on fuel and people than I normally am. You are correct not much affects the great ride of the 500DA! I just started working with the tabs and was hoping to hear from some boater’s with a similar model Sea Ray.

WarrenG
 
I only use my trim tabs when my friends make me take this 450 lb girl out with us. If she is sitting in the back...I am full tabs up, empty the waste tank and cross my fingers. If she is in the front of the boat I always check to make sure my props are still touching the water before I put it in gear. Other then that I almost never use them.

On a side note....the last time she was out with us...I did hit a sand bar that I have never hit before, she clogged up the head and my swim ladder is now "U" shaped. I am still trying to figure out how in the hell she got herself into the head without tearing out the doors.

9yvadyve.jpg


Steve
 
Steve, did she also step on your foot?
WarrenG
 
My boat is pretty stern heavy particularly with 15HP 11" RIB on the swim platform. I have tabs all the way down coming out of the hole and slowly bring them up when I get to cruising rpm until I start losing speed. My boat runs best with some tabs in just about all conditions... once at cruising rpm I experiment a little for best speed. Of course tabs fully retracted for all slow speed maneuvers. Steve, not sure that I understand your post... in what position would your trim tabs NOT be touching the water?
 
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"Of course tabs fully retracted for all slow speed maneuvers."

Thanks for your reply; however I am confused by this part of your response.

WarrenG
 
Trim tabs create alot of drag in reverse when in down position and there is alot of force on the ram. Also, if they are left down and even slightly uneven, you'll pivot on the side where the tab is further down. Bad slow speed handling overall, but particularly in reverse.
 
Thanks for the very useful information.
 
Also, if you leave them down for an extended period of time you can develop growth on them. With my setup, my tabs are down almost full all of the time on plane. Heavy ass and she runs bow high normally anyway. I play with them a bit just to see what affect it has lifting them up as I cruise but see little difference really. When I bought the boat there was 200 lbs of lead shot (in the cloth bags for God's sake!) in the anchor locker. Bags rot out, lead shot everywhere. I am looking into buying all chain for my anchor rode to add some weight forward.
 
Ken, she is not particularly stern heavy just heavy in general, just thought she benefited from some tab. Strangely I am not totally sure till I go out and play some more. This is the largest boat I have owned and I only have 59 hrs of seat time in the 500. I have almost not touched the tabs till last weekend. We boat year round in AZ, so I will continue to experiment and will also make sure I bring the tabs up before backing in the dock. She has no need for tabs to get on plan, in fact bow rise is not a big issue and you never feel it climb over the hump like my other 5 boats I have owned( mostly go fasts).
This is way I am not sure and started this thread. I am somewhat sure she flattens out a bit more and I think I was getting a little more MPH (1 or 2) with tabs down. She tops out at WORT at 34-35.5MPH in Fresh Water. I do not like the wake spray from the tabs however. I have a rope and chain ( 25' ) rode, you can order with 200' or so of all chain, so I will assume it would handle the weight. I am not sure the added weight would be a negative. If you want to use shot or something small and heavy, I would put it in a heavy weight ripe stop type duffel bag.

WarrenG
 
I have found that on my 390 sport fish the more tab the better. Like you mentioned I don't feel the boat go over the hump either. I can definitely feel the boats bow lower when i lower the tabs all the way. My speed for a given rpm rises and fuel consumption on my flowscans goes down. I obviously can't see what the boat looks like but I can see that the bow wave goes from about middle of the flybridge looking down to forward of the base of the windshield.
It counter-intuitive to me why increasing the wetted area of the hull would make it run more efficiently but I have seen it with my own eyes. In my case my boat shares the lower hull with 390EC's and its generally accepted that the trim tabs are undersized.

Hope this helps
 
After adding the hydraulic swim platform and dinghy to the back of my boat, I have to run almost full tabs down. I know this isn't right, so I added 5, 5-gallon bags of water under the front 1/2 of the forward berth. I still need to run with the tabs almost full down, but the fuel flow dropped 3 gph and the engine loads dropped about 3% as well. I have had 150' of chain since I bought the boat and plan to add another 100' for weight and to keep line out of the water (idiots cruise too close to my rode).

This should allow me to use the tabs more judiciously. I considered adding over-sized tabs, and even thought about adding another pair of automatic tabs (the kind that just put pressure down and retract as you accelerate and overcome the cylinder pressure). Adding ballast seems to be the way to go.

Normally, if I run the tabs all the way down, I can feel the bow dig in and the engines work harder. Conversely, if I retract the tabs too much, I can feel the bow rise and the vibration in the boat increases. There is definitely a sweet spot each of us should strive for (when the boat is balanced correctly).

As for retracting the tabs when off plane, I do that for the reasons posted above, however, I find that the boat handles better and has less vibration if I leave the tabs down when cruising forward around 800 - 1000 RPM.
 
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Thanks Guys,
I would love to have even more big boat feedback.

WarrenG
 
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