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I am curious about this device...
I can see where it is useful to have bow down when cruising faster, due to it rising and obscuring view...
is there a reason to this thing set to bow up?
it seems you would always put in bow down position?
is it because it cause drag on boat, and therefore fuel consumption?
I know, a newbie question
Svend
1977 Trojan F30 Express, With Dual 318's with Electronic Ignition
Raymarine EV 100 Auto Pilot
If your are referring to your trim tabs, you are correct, They are used to assist the boat in bringing the bow of the boat down to help achieve plane. They are also used to trim the boat while under way to achieve the most effiecient fuel economy.
On smaller boats, they also help you to level the boat off when your 350lb uncle bob is sitting on the port gunnel.....
You also want to be careful in how far down you set the tabs. If down too far, it can cause the bow to dig in and result in 'bow steer' -- where the boat just wants to fly off to one side or the other without warning. You also want them up a bit higher if you have a following sea, to reduce chanced of stuffing your bow in to a wave.
captainmaniac wrote:You also want to be careful in how far down you set the tabs. If down too far, it can cause the bow to dig in and result in 'bow steer' -- where the boat just wants to fly off to one side or the other without warning. You also want them up a bit higher if you have a following sea, to reduce chanced of stuffing your bow in to a wave.
+1, Captainmaniac is right on the money.
Paul
"Cruise Control" 1978 F-26HT
"No Control" 2012 9' Grand RIB
Think of the trim tabs as being like flaps on an airplane. When on plane you can use them to address a list to one side so the boat runs flat and level. You also (more importantly) use them to help the boat 'fly right' at any given speed. Bow down can be a problem, but too high can also be a problem (with visibility and handling).
You will get used to it over time, but in general : climbing on to plane or running just on plane (probably 2000 RPMish - 10-12 knots), you usually want tabs fully down to try to flatten the boat out and keep bow down (the more parallel it is with the water surface the better it will climb on to plane). As speed increases, you generally want to raise the tabs (let the bow come up a bit) to reduce wetted surface and 'free up the hull', let a little more come out of the water, and counter bow steer. It takes a bit of playing, but you eventually will get the feel for it.
When you are adjusting tabs, don't mash the control.... for the most part, just use little taps to adjust things. Tap it for no more than a quarter to half second, and give the boat up to 10 seconds to respond to the change in dynamics to figure out what adjustment you need to do next. You will find the right (sweet) spots over time... You know you have it right if you have reasonable visibility and no bow steer, and a tap up or down reduces your speed... If you are getting max speed and comfort, the tabs are where they need to be.
Exceptions to the half second tap rule : make sure tabs are full up when at displacement speeds (1800RPM or less) otherwise they are just unnecessary drag. If you want to accelerate to get on plane, put tabs full down. As boat speed increases beyond 10-12 knots, start to tweak tabs up.
When I leave a marina and driving past shore fixtures, what I normally do is go from idle to 1500RPM (tabs fully up). Then accelerate from 1500 to about 2000-2200 RPM (tabs fully down, then push the throttles). This gets me just on plane, with tabs full down to keep the bow down. Next I will advance to somewhere from 2500 to 2800 RPM depending on conditions, and as the boat speeds up I will be tapping up on the tabs.
