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ContinuousWave: Whaler Performance
static trim with jackplate
|Author||Topic: static trim with jackplate|
posted 02-03-2004 04:38 PM ET (US)
Can someone explain how to calculate the change in static trim when using a 5-6" jackplate? It would be very helpful if one could figure out how much extra weight in the rear or on the transom would produce an equivalent change in trim or even how much higher the water level would be on the transom (and how much lower at the bow) after a jackplate is installed. I'm particularly interested in the change for a 150 sport with the 4 stroke 60 hp Bigfoot. I'd hate to buy one and install it and find that the trim has changed so much that the scupper is under water! (No good place to mount a bilge pump in this self bailer.)
posted 02-03-2004 06:35 PM ET (US)
On the older 15s, the static trim changes dramatically with the addition of a jack plate. I think that a formula would be impossible to create--too many variables.
It is my guess that the 25 pound jack plate plus moving the engine back 5 inches is the equivalent to adding 100 pounds of extra engine to your boat.
posted 02-06-2004 04:58 PM ET (US)
Id stay away from the Jackplate on a 15ft. classic hull. Ive got a Yami 4 stroke F60 (245lbs) hanging on my Alert 15 and it sits down in the stern to the point the slash well scuppers are in the water. This is with an under helm steat 15 gal. tank, battery under helm and a ice chest just behind anchor locker in the bow. See difference between my old 1993 GLS I and this new boat from the stern view. Granted the 50HP 2 cyl Evirude is probably about 75 lbs less in weight and the Alert is a heavier fiberglass layup. Still the Alert sits down much futher in the water. The performance is about the same though when run head to head, so the extra 10 hp is used up to make them equivilent performers. Other than the Alerts propencity to porpoise due the extra weight at the farthest moment of the CG.
posted 02-07-2004 03:59 PM ET (US)
I can't answer your question regarding a calculation to determine change in static trim. While you don't say what year your boat was made, I'm assuming it's a newer hull since you identified it as a 150 Sport.
I can tell you what I found adding 6.5-inches of setback on a 1979 15 Sport. I'm using the CMC PT-130 tilt/trim unit with a 1982 Mercury 50hp inline four cylinder.
The PT-130 weighs 45 pounds and provides 6 inches of setback. Throw in another couple of pounds and an extra 1/2 inch of setback for an adapter bracket that was needed to mate it to the screw type transom clamps on the Merc.
When the boat is at rest with 12 gallons of fuel on board, I can't see any significant difference in the static trim. Add three adults - still no difference. No problem either way as far as the splash well drains staying above the water level.
There's a photo in Cetecea of an older 15 foot with a later model 90hp Merc (no setback) - an engine that is definitely heavier my little 50hp. In the caption under the profile shot of the boat, jimh notes that the extra weight seemingly does not affect the static trim.
How closely either of these examples relate to your situation with the 60hp Bigfoot and the newer hull - I can't say. I'm sure there are some on this site who have done something a bit more similar to what you're thinking.
posted 02-08-2004 02:34 PM ET (US)
Thanks for the input--my boat is a new style 2003 150 Sport as you guessed.
All in all, I'm very happy with the boat but (as always) I'm looking for a little more speed.
I found that raising the motor one hole (to raise the anticav plate even with the keel)increased the speed from 35 to 36.5 mph so the idea of a setback and further raising the motor is very attractive.
Note that raising the motor any more without a jackplate will put the cooling water intake perilously close to the surface so I'm pretty much limited to where I am now with this configuration.
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