You are correct sir! The tabs help you get the boat up and out of the water which reduces overall drag.

 

Putting a pair of 30 inchers on mine. Probably won't use much more gas than a blow boat. :smt043

 

That sounds like a great plan, Mike!! We recently brought a hammock out to the dock which the admiral loves to lay in. Now if I get bigger tabs and throw the hammock on the bow, I could take the engines right out!!!


Shaun
Sent from my iPhone

 

Thanks! Glad to know I'm not complete crazy!! Close, though. . I just had a hard time wrapping my mind around how adding drag could improve performance.


Shaun
Sent from my iPhone

 

Next time I haul out I want to increase the tab size too. They are too small for this boat IMHO. The 410DA rides fairly bow high so I would like to make it easier to get up on it.

 

I'm actually surprised at how high my bow rides with the straight inboards. I really would have thought with the engines being more midship, it would have been a bit more balanced. With the tabs down, though, it's a pretty comfortable ride. If they're all the way up I pretty much have to stand to see good. I can sit and have good visibility with them down.


Shaun
Sent from my iPhone

 

Often times running with the tabs down hurts performance, especially in stern drive boats. Some times in inboards they can help. Another experiment to try is leaving the tabs up, but adding rpm. Sometimes a little more speed will produce a better running angle. Sometimes it won't, or you don't have enough engine to get a high enough speed at an acceptable rpm. Play with it with GPS, and a fuel flow meter. You can learn a great deal about the intricacies of your hull/power.

 

I always run with about 1/2 tabs down to get the correct running angle.
The boat just runs better at a flatter angle...the stern is higher and the props are angled more aft pushing us forward better.

I often have run my friends diesel boats.
Formula 41PC with 450 cummins, Avanti 40 express 370 cummins and they also get better speed with tabs down some.
Both of these like 26-27 kts.
So, might not be a lack of power thing...

 

I run with tabs down, but I'm also carrying a lot of weight on the back.

 

When your bow is high you are waisting thrust, if you can lower the bow the thrust angle has changed to utilize this thrust rather then waist it pushing your bow up. I have 300 lbs of chain in my anchor locker to help this effect, but I use to run with full trim tabs to get the best economy, now I run with very little tabs do to the weight in my anchor locker.

 

seems like tabs down could keep you on plane at a slower speed too

 

My folks had a Sea Ray 340 Sundancer of that vintage, and we experienced the same--a little bit of tabs at some speeds would help with the attitude of the bow, and we could see the speed pick up for a given RPM. You can tweak them to find the sweet spot.

 

I know most of you guys are running twins but I have a single engine and I am always fighting it listing to port.
I have the deploy the port tab to get her to ride level, it's a really pain
anyone know how to fix this problem? I was thinking os bigger tabs , mine are only 12 x 18

 

Put a bravo 3 lower in place of your bravo 2.

 

There are no hard and fast rules for tabs. Up, down or partially deployed is going to be one of those hull and weight dependent things. Once you get on top of the water, it's all about the amount of wetted hull or drag. Some hulls have less wet hull (drag) with some tab, others do not. Tabs on those that do not just increases drag and lowers performance and efficiency.

Have fun experimenting....................

 

On Aftica before I even throttle up I put the tabs down. It helps the boat jump out of the hole and I never loose my field of vision. I normally leave the tabs deployed and can rin at 28 to 3100 rpms with a speed of 17 to 20 knots. I took a trip to lake huron few years back and averaged 14gph over the 300+ mile trip. On mine without the tabs down I don't feel it is safe to drive. You completly loose vision and the boat feels unstable.

 

I need to run with tabs 3/4 way down to get the bow angle correct with the 12" tabs I have a set of 24" tabs to put on some day bought them just before christmas it was part of my winter projects maybe next winter. I have experimented with all combinations of rpm's , drive angle and tab positions I get the best GPH with tabs 3/4 down @ 3400 rpm in calm to 1' wind waves.

 

Thanks all. I really struggled to wrap my head around how adding drag could increase efficiency. But the explanations of the "wet hull" area and thrust position of the props makes a lot of sense. It is definitely a whole lot more of a comfortable ride position with them down. If I get better fuel economy too, its a win win!

 

I found that running tabs down get the boat on plane faster and my fuel economy is better if I am going up river against the current. Our boats are designed to run on step, thus achieving the best economy.

 

I run best with my tabs fully retracted, BUT that statement presumes the boat is fully on plane.

At 27mph, my boat wants some tab to stay fully on plane. If you upped your speed slightly, you may find a different imperical answer to your use of tabs.

 

I bought my 1986 390 Express with 454 Crusaders last year. It had the stock 28" X 12" tapered style Bennett tabs. The trailing edge was 23" wide. To get up on plane you had to run quite a while @3600 rpm and maintain 3300 rpm with the 4 barrel's open to stay on plane @22mph. Flow scans showed fuel burn at 3300 rpms to be 34 gph. That's .65 mpg. Over the winter I changed the tabs to 30" X 15" (modified the 30" X 12"). Also modified the old 28" X 12" and cut them down to 12" X 12" and installed them in fixed position at the bottom of the V on the hull. Results: 22 mph @ 3100 rpm, 24 gph (.92 mpg) with 50% tabs (using Bennett indicators). Much more level and comfortable ride. It's like a diffent boat. I have made similar mods to my last 2 boats with similar results. Clearly Sea Ray and most boat manufactuers under tab their boats, don't know why, cost I guess.

 

That's great info and amazing results! I believe from some prior posts I've seen on here that it's possible to change or modify the size of my tabs without having to change out my pump and actuators. Is that right? Mine are flat (I believe), and I like the idea of getting tabs that have the 90 degree angle on the ends, angled down to channel more and thrust out the back instead of off to the sides. This is something I think I want to do...

 

Well I run from Stratford to Port Jeff the other day, pretty calm seas
I can get up on plane with no problem about 3500 rpm,s then I backed it down to 2900-3000
I was able to stay at 2900 rpm, doing 20-21 kts and burning 14.3 gph
I pushed it up a bit to see what would happen and at 3400 rpm's 25-26 kts, and 17.2 gph
2 guys, 1/2 tank of fuel, 3/4 tank of waste ( was cleaning it out ) and 3/4 fresh water
oh just a little port tab to keep the boat level

then on the way back I wanted to see what WOT would be like and was only able to get to 3800rpm and 29kts.
not sure why, I might have had a head wind but will try again to see what happens

 

I was able to stay at 2900 rpm, doing 20-21 kts and burning 14.3 gph
I pushed it up a bit to see what would happen and at 3400 rpm's 25-26 kts, and 17.2 gph

You were more efficient at the higher RPMs ( ~1.43 mpg vs ~1.48 mpg). Not by much, but more effecient non the less. Probably because at the higher speed you had the hull higher up on plane and out of the water a bit more.

 

If your boat is fuel injected, then running the rpm's up to 3300-3500 won't cause a huge increase in fuel burn. The older boats with 4 barrell carbs have the secondary barrell's cut in around 3100 rpm's. If you have flow meters like I do you can tell when the secondaries start to open. It is very beneficial to have the boat run on plane in at a decent trim angle for efficiency and visibility. With gas around $4 or more it's even more important. My 390 last year at full throttle @4400 rpm would burn 56 gph at 33mph (about .59 mpg). Now at 22 mph and .92 mpg I am very pleased.

 

No regrets your engine should run at least 4600 rpm wide open. If not you might need some engine work like fuel filters, tune up. That should help if not you might need compressing test done.