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  1. #1
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    Fisher aluminum 18ft

    I have a 18 foot aluminum Fisher, SV-18CC with a 1990 3cyl 90hp Mercury. It weighs about 700 lbs, the motor is about 280lbs. I have a 24v Minn Kota Riptide mounted on the front, 2 group 31s, mounted up front. Running a turning point Hustler 4 blade 13 by 19. Motor is maxed out 4900 rpm (too low), running at 33 mph.

    When I trim up, it climbs to 36mph and RPMs go up to 5000 but then the boat begins to porpoise and I have to trim back down. I already have a bit of weight up front, I don't want to add more, I want to go faster but I don't want to porpoise...


    Any suggestions?

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    #2
    Most of your weight should be in the rear for best performance, also you need a stainless prop.

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    #3
    Quote Originally Posted by bassfisher444 View Post
    Most of your weight should be in the rear for best performance, also you need a stainless prop.
    I have been moving things all around the boat to try to stop this porposing.

    I also have a 13 x 17 stainless powertech, but prop slip went way up and no speed

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    #4
    As bassfisher444 mentions you need to get as much weight to the stern as possible. I know it seems counterintuitive but tin boats porpoise because the hull geometry, weight distribution causes them to be very difficult to get the bow up and hold it up. I have a Lowe 17HP which is a pad hull but even with a pad the hull won't take much trim. If I trim up much at all, and I've found the lower my speed the less trim it will accept, then the bow just starts to rise and fall and gets into a rhythm. My boat actually runs better with more trim when I have the live-well full because the extra weight in the back helps the center of gravity to move back which helps keep the nose up. I don't know about your boat but a lot of the shorter tin bass boats also have the seating position more toward the middle of the overall hull length than say a longer fiberglass hull. This is so they can allow for as much room as possible on the back deck. Moving the driver and passengers forward really makes it hard for the prop to keep the bow up. Also are you sure about your hull weight of only 700 lbs. My 17' tin hull weight is 990 lbs and I have a Merc 90 2 stroke on it. I am running a Laser II 20p prop and can get low 40s top end on gps and I'm turning 5400 - 5500 rpm. The boat will cruise all day and sip gas at around 33 mph at 4500 rpm. I would think that if your hull is really that light and you're running a 19 prop you would get speeds closer to what I'm getting and for sure a higher WOT rpm. Good luck. I well know that tweaking the set up on a tin boat can drive you crazy. They are very finicky and they just won't take as much trim as a glass hull. If I could trim my engine up and get my bow really up and hull out of the water I believe my hull would hit close to 50 mph but at around 43 mph it starts to porpoise and it gets really wild in a hurry:-)

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    #5
    I have a Fisher Pro Hawk 180 and am running a Merc 125. My boat, minus the engine, is roughly 1800#'s....Ultrex, 4 batteries, deck extension, etc. etc. My boat ran very similar to yours until I installed a 5" HD jackplate. Once I installed the plate and learned to allow the hull to establish itself post coming out of the hole THEN balance trim and the plate all my issues went away.

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    #6
    Quote Originally Posted by Slicefixer View Post
    I have a Fisher Pro Hawk 180 and am running a Merc 125. My boat, minus the engine, is roughly 1800#'s....Ultrex, 4 batteries, deck extension, etc. etc. My boat ran very similar to yours until I installed a 5" HD jackplate. Once I installed the plate and learned to allow the hull to establish itself post coming out of the hole THEN balance trim and the plate all my issues went away.
    I agree with Slicefixer.
    Allison XB-21 ProSport
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    #7
    Quote Originally Posted by PSM207 View Post
    I agree with Slicefixer.
    I do have a Jack Plate, but that might be for a winter project. This boat is older and I would have to set up tilt tube steering

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    #8
    Quote Originally Posted by ChooChooSnakeMan View Post
    As bassfisher444 mentions you need to get as much weight to the stern as possible. I know it seems counterintuitive but tin boats porpoise because the hull geometry, weight distribution causes them to be very difficult to get the bow up and hold it up. I have a Lowe 17HP which is a pad hull but even with a pad the hull won't take much trim. If I trim up much at all, and I've found the lower my speed the less trim it will accept, then the bow just starts to rise and fall and gets into a rhythm. My boat actually runs better with more trim when I have the live-well full because the extra weight in the back helps the center of gravity to move back which helps keep the nose up. I don't know about your boat but a lot of the shorter tin bass boats also have the seating position more toward the middle of the overall hull length than say a longer fiberglass hull. This is so they can allow for as much room as possible on the back deck. Moving the driver and passengers forward really makes it hard for the prop to keep the bow up. Also are you sure about your hull weight of only 700 lbs. My 17' tin hull weight is 990 lbs and I have a Merc 90 2 stroke on it. I am running a Laser II 20p prop and can get low 40s top end on gps and I'm turning 5400 - 5500 rpm. The boat will cruise all day and sip gas at around 33 mph at 4500 rpm. I would think that if your hull is really that light and you're running a 19 prop you would get speeds closer to what I'm getting and for sure a higher WOT rpm. Good luck. I well know that tweaking the set up on a tin boat can drive you crazy. They are very finicky and they just won't take as much trim as a glass hull. If I could trim my engine up and get my bow really up and hull out of the water I believe my hull would hit close to 50 mph but at around 43 mph it starts to porpoise and it gets really wild in a hurry:-)
    Right now I have a 6 gallon tank under the center console and a 6 gallon tank in the rear, I can switch over to a 12 gallon tank in the rear

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    #9
    Quote Originally Posted by leckbass View Post
    Right now I have a 6 gallon tank under the center console and a 6 gallon tank in the rear, I can switch over to a 12 gallon tank in the rear
    That and moving the two group 31 batteries to the back would help quite a bit.

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    #10
    Quote Originally Posted by bassfisher444 View Post
    That and moving the two group 31 batteries to the back would help quite a bit.
    I'm thinking about tossing the 2 31s and putting into lithium's

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    #11
    Before exhausting excessive money and time I recommend checking the running surface (bottom of hull) and verify it is flat. Hooks and/or Rockers (convex or concave areas) along the running surface can create planing issues. I've seen many aluminum hulls with these issues.
    Allison XB-21 ProSport
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    #12
    Quote Originally Posted by PSM207 View Post
    Before exhausting excessive money and time I recommend checking the running surface (bottom of hull) and verify it is flat. Hooks and/or Rockers (convex or concave areas) along the running surface can create planing issues. I've seen many aluminum hulls with these issues.
    That's a GREAT point PSM.....

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    #13
    Quote Originally Posted by leckbass View Post
    I do have a Jack Plate, but that might be for a winter project. This boat is older and I would have to set up tilt tube steering
    IMOP it's got to be hydraulic, at least for me. The sweet spot changes pretty dramatically on mine based on the load and conditions.....feel deal for me. A manual plate wouldn't work very well on my boat.....waste of time if I want to run WOT. I have to balance trim and the plate. Things can change pretty dramatically based on what I'm faced with on a particular trip, even out and back......changes as the fuel in the tank decreases, h20 conditions, etc.

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    #14
    Quote Originally Posted by Slicefixer View Post
    IMOP it's got to be hydraulic, at least for me. The sweet spot changes pretty dramatically on mine based on the load and conditions.....feel deal for me. A manual plate wouldn't work very well on my boat.....waste of time if I want to run WOT. I have to balance trim and the plate. Things can change pretty dramatically based on what I'm faced with on a particular trip, even out and back......changes as the fuel in the tank decreases, h20 conditions, etc.
    If I bought a hydraulic jack plate for this boat, it would be worth more than the boat itself

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    #15
    Quote Originally Posted by leckbass View Post
    If I bought a hydraulic jack plate for this boat, it would be worth more than the boat itself
    TOTALLY get it.....BUT, IF the ONLY way you can get the boat to perform properly is utilizing a HD JP then you've got a decision to make.....

    Mine was chase a prop first or go with the hd JP first. I chose the plate as it would DEFINITELY allow me to operate in shallower h20 (I fish a lot of shallow/trashy water) and MIGHT help solve my porpoising issues. Fortunately it did both for me. As a result I didn't have to chase a prop, etc.

    I also knew I could sell the plate and get most of my money back (bought it for a steal off eBay....lucky).

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    #16
    Quote Originally Posted by leckbass View Post
    I'm thinking about tossing the 2 31s and putting into lithium's
    50ah LifePO4 batteries are 16lbs. each
    100ah LifePO4 batteries are 28lbs. each
    Both are substantially less weight than 2 - 31 series SLA or AGM batteries @ 60 - 70+ lbs. each
    I would still move lithiums to the stern. Keep the bow light.
    BassCat Sabre FTD
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    #17
    Quote Originally Posted by Slicefixer View Post
    I have a Fisher Pro Hawk 180 and am running a Merc 125. My boat, minus the engine, is roughly 1800#'s....Ultrex, 4 batteries, deck extension, etc. etc. My boat ran very similar to yours until I installed a 5" HD jackplate. Once I installed the plate and learned to allow the hull to establish itself post coming out of the hole THEN balance trim and the plate all my issues went away.
    Did you have to move the weight into the back?

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    #18
    Quote Originally Posted by PSM207 View Post
    Before exhausting excessive money and time I recommend checking the running surface (bottom of hull) and verify it is flat. Hooks and/or Rockers (convex or concave areas) along the running surface can create planing issues. I've seen many aluminum hulls with these issues.
    I checked the whole, everything looks very nice, flat and smooth

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    #19
    Quote Originally Posted by leckbass View Post
    Did you have to move the weight into the back?
    No I didn't leck, but, without the plate there was simply no way to run the boat WOT. My deck extension is pretty extensive and weighs probably 75 pounds. That moved the COG forward and caused issues. The extension combined with all of my gear is pretty substantial and it's all forward of the console. Like I stated earlier, the HD plate was a
    miracle for my set up. I'm sure it wouldn't make nearly the difference for most, but, boy it sure did for me.

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    #20
    Quote Originally Posted by Slicefixer View Post
    No I didn't leck, but, without the plate there was simply no way to run the boat WOT. My deck extension is pretty extensive and weighs probably 75 pounds. That moved the COG forward and caused issues. The extension combined with all of my gear is pretty substantial and it's all forward of the console. Like I stated earlier, the HD plate was a
    miracle for my set up. I'm sure it wouldn't make nearly the difference for most, but, boy it sure did for me.
    I have a manual Jack Plate sitting in the garage, I was apprehensive about bolting it onto the back of an aluminum boat. I pulled it off my Pro XL. It would be a straightforward set up, but the steering would be a big pain