21 SOB can't carry the bow.

[Fullthrottleguy]

Hello,
I just got a rebuilt 21' Scorpion/Challanger/Superboat. Loving the boat so far, corners great and is so smooth over waves! The issue I'm having with the setup as purchased is that at about 70MPH it feels like the boat is trying to get up on the pad and fly the bow but keeps falling off. From 70 until 80 it's hopping down the lake no matter how I adjust the engine height or trim. Setup is a 300xs, sporty with 1.62 gears, hydraulic steering, 6" detwiler jack plate, 4 blade 26" trophy. I'm thinking I need to add more setback to better balance the boat and then look into props. The rooster tail is pretty high and long compared to my previous hydrostream. I was going to order a 4" setback bracket for a total of 10" and see how that works.

Anyone care to chime in that has experienced a similar situation or has knowledge setting these boats up to fly?

[vnemous]

Is boat really heavy?? 300xs on a a normal sob should be well in the high 80's+. Whats your rpms with a 1:62 and a 26p Trophy?

[wicheckmate]

maybe a 4 blade with more diameter than a trophy....... and the extra set back should help

[Fullthrottleguy]

RPM is around 6000. Am I correct that 10-12" of setback is the norm / required to make these fly?
boat is fully cored but dry - so it should't weigh any more than the rest of them.

[vnemous]

my tank of a 1976 Challenger ran 80 with 28p Trophy and a 250 efi. Same motor and prop on my 1992 21 super ran 88. 1:72 gears. 21 super has 12" setback with 10" notch. Challenger had 10" setback with 8" notch. Just for comparison. Superboat lighter than the Challenger was.

[Fullthrottleguy]

my tank of a 1976 Challenger ran 80 with 28p Trophy and a 250 efi. Same motor and prop on my 1992 21 super ran 88. 1:72 gears. 21 super has 12" setback with 10" notch. Challenger had 10" setback with 8" notch. Just for comparison. Superboat lighter than the Challenger was.

Interesting... I didn't realize they had different transoms. This one is flat right down to its 6" pad, so I'm thinking some more setback will really help it. Come to think of it I guess my old hydrostream had a notched transom in addition to its 6" plate - and that boat was waaayy lighter.

[vnemous]

They were both altered bottoms by Raybo Marine in Long Island.

[XstreamVking]

Where's the fuel tank? Ahead of the 1/2 way point of the boat? Or behind? Under bow? Weight fwd makes them ride good. Weight back makes them faster.

[vnemous]

Most are a 60 gal belly tank starting at bulkhead of back seat up to the front of the front seats.

[Fullthrottleguy]

Most are a 60 gal belly tank starting at bulkhead of back seat up to the front of the front seats.

This is where mine is. I'm not sure just how big it is but its BIG. I ran for 3 days and only use 1/2 tank!

[XstreamVking]

Start by just running a 1/2 tank when out for just the day. Not carrying the xtra 30 will help some. That's a 250 pound weight reduction right there. Set back would be a good thing for this boat. IMO You have the best guys at making them run fast on here, so they know what will work best for you.

[Fullthrottleguy]

I went ahead and added a 4" bobs setback bracket, so now I'm up to 10" total. Boat ran 90 with a 28 Mazco on the limiter. It still needs more setback and prop as it still won't carry the bow with a passenger, but this is a step in the right direction. I see 95 in its future next year.

[RobF]

Take off the trailer, check the bottom to see if it's straight
do you have a floor under the bow?

[Fullthrottleguy]

bottom is straight and strong. Yes there is a floor under the now and the boat seems to be somewhat overbuilt, including core up the sides and on the deck from the steering wheel back.

[2.5-21]

What is actual boat? who built it and what was done to re/do it? Post some pictures

[RobF]

bottom is straight and strong. Yes there is a floor under the now and the boat seems to be somewhat overbuilt, including core up the sides and on the deck from the steering wheel back.

remove the floor

[2.5-21]

Curious to what brand it is and who built it, There are a lot of copies out there.

[Fullthrottleguy]

Turned out to be the very very first TUFF 21, prior to them altering the design from the original Linder one.