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Old 03-21-2015, 09:12 PM   #21
Capt.Bill11's Avatar
City: Sarasota/Ft. Lauderdale
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Originally Posted by twistedtree View Post
I beg to differ. Our Grand Banks was a planing hull and definitely benefited when on plane.
Your on plane speed is not the same as a SF running 30+ knots.

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Old 03-21-2015, 10:11 PM   #22
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Originally Posted by Capt.Bill11 View Post
Your on plane speed is not the same as a SF running 30+ knots.
No, 20 kts.

The trade-off, as I understand it, is that to optimize for lower speed you would use larger fins to gain more lift. But at higher speeds, those larger fins mean greater drag.

To optimize for higher speed you would use smaller fins to reduce drag. Getting enough lift at speed is not an issue - the fins move very little compared to slower speeds. But at lower speed the smaller fins will reduce effectiveness.

So you can have both, but you still need to decide what tradeoffs you are going to make. I went with larger fins for effective stabilization at 6-10 kts, and accepted the greater drag at 20kts. But the impact on top speed was negligible - maybe 1/2 kt.

Re Andy's point, on boats that have a larger speed range, ABT fits a shaft speed sensor so the system knows how fast you are going, and it automatically adjusts accordingly. No tuning is required. My Nordhavn has the speed sensor too, though it's not as important to have as on a faster boat.

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