Flaps set up

[robymayway]

I have a question about Flap position.

hatt conv 37" 2 x 325 dd

shipping at 2000/2100 rpms and speed around 19 knt/20knt I notice that if flaps go down totally, the boat reduce speed at 17/18 knts.
Than, reducing a little bit the angle of flaps, speed return at 19/20 knts.

What happen???
I see that with flaps opened completly, the boat move a lot of water more. It's normal? Which is the correct position of flap???

The maximun range of opening of my flap is around 5 centimetres. Is normal?

Thanks and sorry for my bad explication

roberto
Italia.

 

[REBrueckner]

The correct positon of your trim tabs is the one that gives you maximum speed. That position will vary depending on the total load in the boat as well as the distribution of the load. A full load of fuel, with mostly stern tanks, will likely require some additional tab angle relative to full water, if the water tank is forward, and let's say half full fuel tanks....With fuel and water roughly 8 lbs/gal a 250 gallons in aggregate gets close to a ton in weight.

Also trim tab angle might vary a bit between fresh and salt water as the latter is more dense...and if a boat has added fixed strakes or spray rails/lift rails they generally provides additional lift....

 

[Pascal]

i always use the GPS to adjust the trim tabs for best speed... it depends on the load, the boat, the power setting, etc...

usually, as speed increases you need less trim tabs to get best speed, since the drag increase with speed. at lower speeds (on plane), you often need more lift so you need more tabs.

start with full tabs to get on plane quickly then once you're at a set RPM, reduce tabs until speed peaks.

 

[sandspur1966]

Especially when on final approach!