Trim Tab Question

[tony p]

I have only run my blackman a few times (26 billfisher bought from Charlie), but a novice question on the trim tabs. i am running the engine tilt at -4 or -5 and had the bow all the way down and it ran terrible - very squirrely and low speed. The boat would pull real hard to one side or another - no a pleasant drive. This afternoon on the way in I kept the engine trim at -5but used the trim tabs to tilt the bow almonst all the way up. It was not squirrely and speed went way up (19-22 knots at 3200 rpm). Any suggestions on optimal tilt?

[DOGHOUSE26]

A Blackman is more efficient @ speeds < 14-15 knots with the tabs all the way down, but after that the boat wants to get higher out of the water so you need to start backing off the tabs; by the time you hit 20-22 you should have a minimal amount of trim tab. But the cardinal rule is always leave your tabs up higher in a following sea so the bow doesn't bite in at an angle and suddenly turn to one side, very dangerous.

[tony p]

when you say "all the way down" I assume that means in the bow down position. Minimal tab means the tabs in the bow up position? Higher tabs also means bow up? This winter it has definately been a bigger swell so I have had some bigger following seas. How big a swell should I be concerned? I have had a few experiences with a quick lurch to one side - and i definately did not like it! I think I had by bow dug too deeply down. the ride seems much better with the bow up.

Does the trim of the moter make any difference?

Finally by efficency i assume you mean fuel. When offshore for tuna that definately makes a big difference. When shooting out to la Jolla I'd rather burn a few extra gallons for the time savings, but is there anything else I should be aware of on efficency?

[Malu Lani]

Steve Blackman told me when the wake starts even with the helm seat the trim is right with the tilt at -5. I cruise at 3200 rpm and count to five seconds on the trim switch this gives me 17kts at 2.5 knot mi per gal tilt at -5.Play with the tabs at a good rpm and find the sweet spot.I think every boat is different because of weight and hp.I think the same for the down swell handeling.I remember the learning curve well by the end of summer you will be a pro.

[Honeygirl]

Although ever boats different. If your boat is squirrely at any speed you have the bow dug in to deep. I normally run at 20-24knts. The trim number on the outdrive of every boat is different while I run mine at negative 2 and Zack runs his at negative 7 you may need to run yours at 0 or some other number. I also run oversize trim tabs and under speed, loaded I push my tabs down appx. 2 secs. In a heavy following sea my boat runs best with a heavy tab at around 18 knotts. But the ride is a little wetter. Your best bet would be to go out and run it and play with your system.

P.S. during normal running 20-24 knotts I average 2.25mpg

[DOGHOUSE26]

On most drives -5 is the bottom, but it's really relative to each boat and to the calibration of the trim sender switch. Actually I think the boat rides better in the 0 position or straight up and down when the boat is on a plane; when you're the trailer check out the relationship between the drive and the boat's angle of position. The problem was my trim rams would never hold the drive in the same position all day they would always end up @ -5.

You can feel/hear the props cavitate if the bow is too high; and if you're too low at cruising speed your boat will do slow "S" turns on auto pilot as the boat digs in at the bow and turns ever so slightly. It just takes practice.

[yellowfin1]

On Tenacious, my 280 OD tilt is always run at -3 (which is where it bottoms out). At cruise I usually keep the trim tabs pretty much level which gives me the best economy (verified by flowscan). Of course we rarely get perfectly flat seas so, you'll want to adjust the trim tabs to try and get the best compromise between economy and a comfortable ride. Strait into a choppy sea, you'll want the bow down.

[Time Out]

Wow thats alot of info for a newbe

I only have one thing to say when you come into Mission Bay the rule is BOW UP No trim tabs at all Keep your speed down and come in on the North side of the Jetty in a big swell.

The rest you will leard in a short time. If you ever need someone to go out with you let us know it cant hurt.

Russ

[Knot Now]

Steve Blackman told me when the wake starts even with the helm seat the trim is right with the tilt at -5.

I run my boat at 3200 rpm with the white spray from the wake even with the helm or just behind.....tilt trim at -3 to -4
I will have the bow down more if I am going into the swell at a much lower speed...10-12 kt.

PS if you ever want to go for a ride or have one of us come along, just post an email or...

[tony p]

Wow - thanks fo rthe info and I definately will take some along for ride alongs and advice! This really helps. I now know that I am not crazy and the bow does dig around and get squirrely if I am going too quick. I am also glad to hear that Honeygirl goes in the low 20s with 2.25 mpg. I know my boat can do that speed (seas willing) - now I just need to dial in the trib tabs. (My friends grady gets 1 mpg in the mid 20s!!)