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Seriously off center
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Discussion Starter #1
Is this normal for flatbottom jets, and should I raise or lower the cav plates to try to keep it loaded?
 

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Seriously off center
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Discussion Starter #3
It's an 18' 1965 Stevens flatbottom with a .060 over 10:1 390FE, Berk JA with a A impeller. As soon as I open up the secondaries at speed it blows the pump out. It turns between 47-4800 rpm if I slowly squeeze into it.
 

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In 1965 the jet drive was just starting to come into use in the consumer market. Mfg's like Stevens were all geared up for v drive boats so when the jet drive started to become popular they tried the jet drive in a hull that they already had rather than tool up a new boat designed for the jet drive. Well guess what you are the owner of a classic but the hull was desiged for a v drive so the vee is to shallow and the and the bottom is almost completely flat so ride and performance will never be acheived in this kind of hull. Crusing and skiing are a possibility but top end performance is going to be a real challinge.
 

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Boat Nut
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5,131 Posts
This sounds like the RoostWear's Boat, he was looking into a loader to keep that from happening. The loader was a little different from the common 12JG series loaders, it was bolted on at both ends vs just one end. A loader probly won't solve the problem 100% but it certanly can't hurt you any. Now to to find one, or a builder for one, good luck.
 

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Seriously off center
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Discussion Starter #6
That is my Stevens. When Hotboat imploded, I figured since Roostwear is long gone, there was no need to continue the name. I now have a more fitting name :D
I know there's more in it otherwise I wouldn't be able blow out the pump at will. It's just a matter of finding out the secret from someone that was around when this thing was new. The ads bragged it did 70 mph, and I guess it's just my nature to try to eek out a bit more. I have a ramp loader in it that Victorfb loaned me and it helped a little, but what gains I've made so far have been by dropping the plates to bring the bow down. The exact opposite of what I'd do on the Advantage.:confused:
Greg's right.... this is a very cool cruiser. I actually enjoy it more than the Circus Boat... on the weekdays. I never would have thought a flatbottom would handle crossing wakes better than a hull with more V.
So is there any more in it by working on adjusting the cav plates?
 

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Boat Nut
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5,131 Posts
Well there is the idea of keel loading, a spoon, or bump, infront of the pump inlet. A deeper keel prior to the inlet, will stay in contact with the water. You certainly don't want to plow around the lake all day.
 

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Seriously off center
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Discussion Starter #8
Modifying the keel in front of the intake may help, but the reality is that this hull will never really "work". It's a great cruiser and not a long term project, so I'll be happy if I can get more out of it working the setup.
Oddly enough, it really doesn't plow much because the bottom is flat. It may scrub some speed, but this thing has REAL nice manners when you shut down abruptly.
 

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Boat Nut
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Thats the beauty of a flat bottom, it won't lay over, and turn. You may find with this hull, your hardware needs to hang down, below the keel, in order to load properly. I love the look of your Stevens by the way
 

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Seriously off center
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Discussion Starter #10
The loader Vic loaned me sits about 1/4" below the keel. Choppy water is not really fun without a rev limiter
 

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Seriously off center
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Discussion Starter #11
Thanks for the compliment. The winter project is to get the teak side steps and new fenders on the trailer.
 

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mo balls than $cents$
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11,734 Posts
is your loader ramps directing water correctly? i've got a nice loader that's "factory made" pro loader that absolutely blocked off the top flow of water to my impellor(dominator 12s pump). be sure its feeding water where it should, all loaders aren't created equal!
 

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In 1965 the jet drive was just starting to come into use in the consumer market. Mfg's like Stevens were all geared up for v drive boats so when the jet drive started to become popular they tried the jet drive in a hull that they already had rather than tool up a new boat designed for the jet drive. Well guess what you are the owner of a classic but the hull was desiged for a v drive so the vee is to shallow and the and the bottom is almost completely flat so ride and performance will never be acheived in this kind of hull. Crusing and skiing are a possibility but top end performance is going to be a real challinge.
Curious..
My buddy runs a Hondo V-drive Hull with a pump in the mid 80s with a mild built 496. What is the difference in that hull and the Stevens? Is it just the deeper V?
 

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Seriously off center
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Discussion Starter #14
Well, the Stevens is a true flat... no V. There's no V to cut the water and keep the intake loaded. If you picture chop as a series of highs and lows in the water, a V would cut through the highs whereas a flat would try to ride up over the highs (with the air from the low passing under the hull). A prop sits below the keel and is still in the water as the hull lifts. If a flat lifts, the intake takes in air.
At least that's my take on it.
 

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I don't have any real answer for you other than to tell you a flatbottom jet can be optimized.

A friend has/had a 1970 Mandella (lost touch) 18 ft short deck w/ a berkeley pump. It's a flat bottom (2%). The jet stuck out stubby exactly like your. It ran an LS-7 chevy motor in it. One of the few jet boats Brummet made. I skied behind it many times and rode in it a bunch. The thing absolutely ripped out of the hole and ran to 6K. Cavitation wasn't an issue at all. Period. This is not rumor. I rode in, skied behind and drove this boat many times. Smooth water and chop. Fyi-- 3400 was ski speed (somewhere around 33-36 mph-- I'm positive it ran 65 mph at least. It was faster than one of the vdrive mandella's in the group that ran a 392 hemi. It (hemi) was a pure ski mandella that had fixed plates and ran 60 at 5000 rpm. That boat is still around.

Only thing scary about it (jet mandella) was that a skier could drag the boat all around when you were cutting. I mean ALL AROUND- and don't you dare pull out (skier) as the boat was making a 180 to head the other way. Give the driver an absolute heart attack as the boat was swapping ends... Mucho water over the deck one time. It had a rudder attached at the end of the bowl as well. You kinda got used to a full turn of the wheel to compensate for the skier cut. With a good skier, you could catch a rythm with the steering wheel. Really weird, looking back. Don't remember about the boat's cav plates.. I know it had something, cause I don't rember any big deal getting in the boat after skiing. Just not sure what they were.

Good luck-- the answers are out there. I just don't have any. Sorry.
 

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Seriously off center
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Discussion Starter #16
I don't know if the answers are out there or that I'll just have to figure it out for myself.
It was interesting reading your experiences. I haven't pulled a skier yet (no ski tow), but one thing is for sure... you drive this boat with your right foot WAY more than a normal jet. Turning is an adventure, and if it didn't have a turning fin it would a LOT harder to turn.
The old Stevens ads said they did 70 mph and I don't doubt it. It goes 55 just on the primaries of a 750 Holley, so it's not shy on hp. If I can just get it to stay loaded on the secondaries I'll have found the secret.
 

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mo balls than $cents$
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I don't know if the answers are out there or that I'll just have to figure it out for myself.
It was interesting reading your experiences. I haven't pulled a skier yet (no ski tow), but one thing is for sure... you drive this boat with your right foot WAY more than a normal jet. Turning is an adventure, and if it didn't have a turning fin it would a LOT harder to turn.
The old Stevens ads said they did 70 mph and I don't doubt it. It goes 55 just on the primaries of a 750 Holley, so it's not shy on hp. If I can just get it to stay loaded on the secondaries I'll have found the secret.
does it have any shoe or ride plate? wonder if a bolt on kit like you used on the circus boat would help???:)bulb
 

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Seriously off center
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2,439 Posts
Discussion Starter #18
does it have any shoe or ride plate? wonder if a bolt on kit like you used on the circus boat would help???:)bulb
No shoe, and it has cav plates instead of a ride plate. Gotta remember the intake (and consequently engine) is a good 12" forward of a "modern" hull setup. I think unless I change my mind and try modifying the hull, I'm locked into loader and cav plate changes. Thing is, setup on this is the opposite of a normal jetboat and it's hard to get my head around. I think I need to DROP the plates to lift the transom and bring the bow down to load the intake. On the Circus boat, I'd lift the hull to dry it out. On this, that's the LAST thing I want to do.
 

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mo balls than $cents$
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11,734 Posts
No shoe, and it has cav plates instead of a ride plate. Gotta remember the intake (and consequently engine) is a good 12" forward of a "modern" hull setup. I think unless I change my mind and try modifying the hull, I'm locked into loader and cav plate changes. Thing is, setup on this is the opposite of a normal jetboat and it's hard to get my head around. I think I need to DROP the plates to lift the transom and bring the bow down to load the intake. On the Circus boat, I'd lift the hull to dry it out. On this, that's the LAST thing I want to do.
ohh, gotcha. intake is just too far forward.might holla at scott seastrum, he's making these wolf fang loaders that work great on probs like you're having.
 

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031
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655 Posts
Back in the early 80's I had a Mandella flat with a 410 Merc and Berk jet. Thatsthing would spin in a heartbeat, then slide backwards until the cav plates dug in. You had better be on the gas when they did. Never sunk it but sure got a lotta water in it a few times. The cool thing about it was if I got weeds or grass in the pump I could pull the cover & clean it out without having to beach it.
 
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