FS 17 Jack Plate Mounting

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rbecker08
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FS 17 Jack Plate Mounting

Post by rbecker08 »

Hey all, so finally starting to put stuff on it. Building a FS17 ls and attached a jack plate to mount the engine to the transom. I don't have the actual motor to go on the boat yet, any guidance on how far up the transom to mount this. Attached pictures if it helps but I should have 3 inches of total adjustability so could be 1 in off either direction (up or down) and be okay. Thoughts?

For the backer boards I saw the need for two backer boards on the plans but any guidance on size for these and should they be epoxied to the hull or glassed in? Thanks and we are getting there.
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BarraMan
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Re: FS 17 Jack Plate Mounting

Post by BarraMan »

A good question, for which I don't have a good answer! :doh:

If the starting point is the cavitation plate level with the keel at the transom, then 1" up for each 12" of setback by the jack plate. Maybe that is a place to start but it generally goes to trial and error from there. I just seem to crack it with my hydraulic jack plate, which has an 8" setback! I generally run with the plate right down and only lift it for skinny water.

I fixed my jack plate directly to the transom with just a layer of silicone sealer in between.

rbecker08
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Re: FS 17 Jack Plate Mounting

Post by rbecker08 »

BarraMan wrote: Wed Feb 01, 2023 12:03 am A good question, for which I don't have a good answer! :doh:

If the starting point is the cavitation plate level with the keel at the transom, then 1" up for each 12" of setback by the jack plate. Maybe that is a place to start but it generally goes to trial and error from there. I just seem to crack it with my hydraulic jack plate, which has an 8" setback! I generally run with the plate right down and only lift it for skinny water.

I fixed my jack plate directly to the transom with just a layer of silicone sealer in between.
Thanks that helps a lot it gives me a target to shoot for, I guess I am hoping there is some standardized distance from cavitation plate to the bottom of the mounting bracket. I am really just trying to make sure i put the bracket in a spot where i render the boat problematic.

fallguy1000
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Re: FS 17 Jack Plate Mounting

Post by fallguy1000 »

Jack plates are typically installed in the same place you would mount the outboard or same rigging holes as ob.

An exception would be if you have the bottom of the splashwell in the way, with a limit that you don't want to mount the plate up so high that you have any chance for shearing the top bolts out.
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fallguy1000
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Re: FS 17 Jack Plate Mounting

Post by fallguy1000 »

Then a plus 6" plate (up) can be used to install at 25" motor on a 20" transom, for example..
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TomW1
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Re: FS 17 Jack Plate Mounting

Post by TomW1 »

The FS17 does not need a jack plate as it is a V-hull with a draft of 8" including the skeg. What are you hoping to accomplish with the jack plate, I have only seen one and that was one a 4" on an FS17LS. If you think you must have one falllguy is correct since this is for a V-hull and you will not be able to use the hump created by the tunnel, mount it the same way you would the motor. The other thing you will need to take into account is moving the motor back. Let's call the bracket length x and you are adding a 50HP Yamaha motor is 250lbs without prop. So, as an example if your set back is 1', 1' x 260lb is 260lbs, 6" x 260lbs would be 130lbs are the amount of weight that you will need to move forward of LCOG.

Well I hope this makes sense and you reconsider the jack plate on your FS17 unless you have already built it without the motor well.

Tom
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rbecker08
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Re: FS 17 Jack Plate Mounting

Post by rbecker08 »

TomW1 wrote: Wed Feb 01, 2023 1:34 pm The FS17 does not need a jack plate as it is a V-hull with a draft of 8" including the skeg. What are you hoping to accomplish with the jack plate, I have only seen one and that was one a 4" on an FS17LS. If you think you must have one falllguy is correct since this is for a V-hull and you will not be able to use the hump created by the tunnel, mount it the same way you would the motor. The other thing you will need to take into account is moving the motor back. Let's call the bracket length x and you are adding a 50HP Yamaha motor is 250lbs without prop. So, as an example if your set back is 1', 1' x 260lb is 260lbs, 6" x 260lbs would be 130lbs are the amount of weight that you will need to move forward of LCOG.

Well I hope this makes sense and you reconsider the jack plate on your FS17 unless you have already built it without the motor well.

Tom
The LS version doesn't have a motor well or I have some head scratching lol. But really I am hoping just to allow for some flexibility with getting the motor height right, that's it. I don't have a motor so if I mount this close enough I can still get everything aligned correct. It gives me some margin for error with a setback of 4 inches. I will be going with a lighter motor.....20 to 30 hp. I'll weigh the boat when I am done to start figuring that out on how lite I can go.

This is also why I put the battery and fuel under the front deck.

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Re: FS 17 Jack Plate Mounting

Post by fallguy1000 »

Jack plates offer a lot of flexibility. Mine is shooting water all over; needs a bottom cover.
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OneWayTraffic
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Re: FS 17 Jack Plate Mounting

Post by OneWayTraffic »

The COG change is pretty relative, 130' would only need to be moved a foot, or 26' five feet.

I'd suggest you rethink the 20hp though. 30 minimum would be my suggestion, or if you plan to use a tiller. 40hp if you want to plane out with a heavy load and take a skier.

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Re: FS 17 Jack Plate Mounting

Post by mineratt »

I will be installing a jackplate on my FS17 (I have not done it yet). I drilled the two upper holes right where they are supposed to, this placed the two lower holes in an awkward place. The jackplate will allow me to adjust the location of the two lower holes and then to adjust the height of the outboard (maybe my measuring is not good enough, I always need to fine tune things a bit once its all up and running). Flexibility in the bolt location, and adjustability.

I had a 78 Dusky 17 open fisherman that would vent on sharp turns and the outboard did not have enough negative trim, the jackplate let me lower the outboard an inch to stop venting, and after a bit a set of wedges helped with the trim. I currently have a Boston Whaler 17 and the lower bolts were installed poorly when i got it. I relocated the lower bolt holes with a jack plate. They are easy to install, do not weigh much, with light outboards they are pretty rugged, and they allow for flexibility.

The only real issue would be with respect to the effect of moving the weight of the outboard aft by 6 inches, in the Dusky it did not affect the trim at all (but that boat was exceptionally heavy), with the Boston Whaler I did not notice anything different either.

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