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Thread: 300xs setback question
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11-04-2019, 04:07 PM #1Member
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300xs setback question
I currently have a 21’ v bottom with a 300xs on a Bobs 12” hydraulic jackplate with an added 3/4” plate in between the engine and jackplate in order to use the trim indicator mount for the engine.
The boat has a porpoise in it at 30-45 mph that it never had before with a 260 and 6” setback. (Big weight change since the engine swap)
The absolute most I can shorten the setback would be to change the jackplate to a 10” and take out the 3/4” plate.
Would moving a 300xs (500lbs) 2 3/4” further forward to the hull help with this?
I’ve tried a handful of different props to see if that helps but the porpoise is there with all of them.
I appreciate your time and input. Thank you.
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11-04-2019, 06:34 PM #2
I'd have to say to much set back with the added weight , if u could get it to sit in water like it did with 2.5 or just little deeper u can prob eliminate some of it. but only way is shorten plate. Possibly move battery up front and lose sum set back if u run 6 in with 2.5. u need a 3 or 4 in with 3.0 I would think
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11-04-2019, 06:59 PM #3Member
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I agree. However, The closest I can get this 300xs to the transom would be just shy of 3” closer than it is now. I would assume moving a 500lb engine 3” closer to transom would help somewhat with the porpoise you think?
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11-04-2019, 07:08 PM #4
Yes. I think anything will help. I know 2 or 3in out helps so should help same reversed. I'd think. do u have plenty bow lift
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11-04-2019, 07:24 PM #5Supporting Member
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Its always easier to counter balance a boat with too much set back then not enough. Throw 20 pounds of "secured weight" in the bow and start testing. Add weight as needed to get your desired result. You now have the torque and power to carry the bow even with additional weight up there.
Joe
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11-04-2019, 07:27 PM #6Member
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Yes. Bow lift is there. Just this added weight has made a perfect all around boat start to porpoise at play ski speed and in turns. I just hope a 300xs 10” back will be near the ballpark of a 260 6-8” back. I know thats a big difference ha. Just wanted to see if you thought 3” would be worth trying.
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11-04-2019, 07:35 PM #7
Last edited by Merc 2.5; 11-04-2019 at 07:38 PM.
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11-04-2019, 07:37 PM #85000 RPM
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I had a challenger with a 300xs 20" and a 11 1/2 setback and never had a problem with porposing.
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11-04-2019, 08:01 PM #9Member
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Not worried about top speed as I am having an overall boat. My plan was to put the smaller jack plate on it and yes, counter some weight if needed, with a little weight up front.
It’s probably a little lighter boat than your old challenger and then, has a 40gal fuel tank in the back along with the battery pumps etc.
Just wanted to get some input on the smaller plate and then if needed, sounds like some weight up front would assist.
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11-04-2019, 08:08 PM #10
Then joe is right if not worried about top speed. Throw few sand bags n front and c how it does. I'd do that b4 I changed plate
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11-04-2019, 08:32 PM #11Supporting Member
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Its really easy to try and you will find that balance can be corrected without going through the headache of changing everything. When you don't have enough set back, its a much more complicated problem. You can also run a thru hub propeller if you are not already "promax" and the barrel will help carry the additional weight on the transom.
Joe
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11-04-2019, 08:49 PM #12Member
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I tried Bravos with both the flared hub and one with it cut. Zero difference. I like the handling of a through hub prop like a Bravo.
Boat has plenty of bow lift.
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11-05-2019, 08:57 PM #135000 RPM
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If you have plenty of positive trim for running fast, you might consider using some 2-1/2 degree negative wedges between the engine and setback plate. It should get rid of your porpoise and may even give you a bit better hole shot with the additional tuck. I have a 21 footer with 18" of setback.
Last edited by lance; 11-06-2019 at 09:47 AM.
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12-12-2019, 12:26 AM #145000 RPM
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I’ve ran 10, 12, 17, 18, 24 and 30” setbacks. Not cause I wanted to buy boats had them. Lol stainless marine or Gil bracket and cmc setbacks w jackplates.
Bar none bbanfs down best set back. PORTA BRACKET.
I LIKE THE 17” myself lol
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