jets and steps

[glassdave]

Hi guys. i havent been on in a looooong time. you guys helped me out with a 23.5 foot Mirage daycruiser project i had several years ago. got me a new project i'm thinking about doing. i have been racing a 24 foot Reindl Batboat(see pic) for a few years now and am thinking about building some new ones here in ohio. as a pet project i was thinking about laying up a very light carbon fiber/kevlar hull and droping in a jet and big block just for fun. my question is does anybody have expierance using a pump on a hull that is steped. i have a local friend that is a ace jetboat guy (JetTech i think is his company) and has been building bigtime drag jets for a while. just took a 100+ mph ride with him sunday in one of the "pleasure boats" he built. i'm hoping he will help me with the details as his knowledge and rigging is second to none. anyway i just thought i would put the question out on a forum and see if anyone else tried to put a jet behind steps. thanks in advance all.

[glassdave]

batboat pic

[glassdave]

heres some pics of when we blueprinted the bottoms last winter

[glassdave]

oh by the way we have already discussed a major rework of the bottom for this project so any suggestions on what to change or where to start would be greatly appreciated. i have even considered building a one-off hull without steps altogether but would like to keep them if possible. thanks again guys

[LVjetboy]

I'm no expert but pumps like clean water. So I suppose how well it works depends on how far back from the step the intake is located, or if there's a center pod or section leading up to the intake that's step free and/or slightly lower than the out board stepped surfaces. What's your speed goal?
jer

[glassdave]

dont really have a speed goal yet but the faster the better ya know. its mostly a project just for fun an whats more fun than a jet. i get alot of looks and attention at the docks when i take the race boat out on the river. been out to dinner at the river front more than a few times with it. i just think it would be really sweet to have a big ol' roostertail shooting out the back of one of these. theres no center pod on these they are a 22 degree v hull and we have discussed making somthing like that to assist laminar flow (somthing i learned about talking to my local tech guy)

[LVjetboy]

Looking at your hull shots, w/o mods seems your pump may suck aeriated water at least from that last step... depending on speed. Are you considering removing the center section of one or both steps with a center pod extending forward of the intake? Maybe a small hit in drag but worth it for clean water?
jer

[glassdave]

LV- thanks for the reply. i agree without mods i dont think it would work at all. this i a very airated hull and works unbevieviably well for rough water performance but not so well with a jet of course it was never intended to. in the back of my head i am thinking i may have to do one without the steps an thats why i thought i would run it by the forum. as a starting point im shooting for a 1000-1200 lb. bare hull weight and a 650 hp 540 BBC. i probably wont start laying glass till this fall and i wanted to get all my ducks in a row first. thanks again
by the way can you post photos in the replys here ?

[LVjetboy]

You can post pics like this...
http://members.cox.net/lvjetboy/BatBoat.jpg
If that's what you mean.
As for doing one without steps, I was thinking more of just modified with a center pod but still stepped outboard of the pod. The width of the pod may only need to be 3 or 4 inches wider than the intake on either side but at an elevation inline with the most forward step. You may get a bit more drag at speed but still benefit from steps outboard of the center pod. The center pod at that depth would also help keep the pump loaded in the rough although I don't know what it would do to lateral stability as speed goes up. But I'm thinking where you boat (I've jetted Lake Erie too) if you're running a true 650 hp with a pump you'll need help staying loaded, steps or no steps.
jer

[LVjetboy]

BTW, sounds like an excellent project for HBM coverage if they're reading this.
jer

[glassdave]

thanks LV. thats actually along the same lines my tech friend was thinking, i am out of my element when it comes to jets. i am going to take some measurments to see just how much rise there is from the rear running surface to the front step. i think its only about 3 or 4 inches so it may not be to bad. i just remembered that the inner most chines are almost a concave surface between the two and about a foot wide so that might be somthing to work with. it would be cool to get in HBM with it.
yea, thats what i meant on posting the pics. how do you do that.

[FoMoCo]

I am not an expert By far, but I had a friend that was running a 21ft Eliminator Scorpian Hull with a Blown Big Block chevy and a Berk JG pump in the stock location. From what I remember these hulls are stepped and meant for outboards. That boat looked sweet, handled Sweet, but it did not perform so well. It would work OK form outa the hole and cruising around. The problem was really when you were in it and then let off, the boat would set back down and airate the hell out of the pump and it would cavitate like crazy, so bad in fact he would have to slow WAY down before the cavitation would stop!!! :squiggle: But maybe the center pod Idea would work :confused:

[UBFJ #454]

The hull you have in your pictures is, in no way shape or form, suitable for a jet drive ... I strongly suggest you research jet hulls and how they work a lot more before going any further with your thought of putting a jet drive in your "Bat" Hull ... Your hull looks Great for an I/O, V-Drive or, an OutBoard ... Just Not A Jet Drive.
We're looking at steps on our new drag boat hull ... I think they'll work well if integrated into the proper hull at the right spot(s).

[glassdave]

thanks for the replys guys. this is a project purely for fun. ragged edge performance is not my ultimate goal. if it dosent pan out i can always go back to an I/O. just looking to do somthing alittle different. these things are an awful lot of fun to tool around in. any time i pull into a gas station i have to set aside about 20 minuets to talk to people.
Bear-i guess this is part of my research on jets. I agree its unsuitable for a jet in its current form. i am in the process of building a fresh set of molds for these boats and thought i would see what it would take to set one up for a jet. i am fully capable of building a custom running surface for this one boat even if it means loosing the steps altogether. i am just unfamiliar with jet running surfaces so i thought i would start by poking around online and see what i could learn before i got in too deep. what kind of hull is your drag boat and what kind of drive? just curious. thanks

[UBFJ #454]

dave -
Jet Drives work best in Air Entrapment Hulls of which there are quite a few different types of schemes used to trap the air to provide lift. Jet Drives do not work well at all in Displacement Type Hulls such as V-Hulls, especially Deep V's such as the one in your pictures. There are a few shallow V-Hulls with some outboard air entrapment that jets have been installed in and are reasonable in terms of their performance.
Our hull is a 19 ft. Race Modified "Old" Brendella "Pickle Scoop" Jet Hull with a Dropped Race Keel ... It has aspects of a Flattie, a Hydro and a PickleFork Tunnel all rolled together into it ... The individual aspects of the various different designs all come into play at different speeds and, in fact, it is these differing characteristics is the reason that we choose the hull for our Progams starting point. The Bare Hull weighs 500 +/- 10 lbs. (w/the pump intake installed).
When we can find the monetary support to build our next generation hull, it will be siimilar, but, different (if that makes any sense) in many aspects ... One thing is that it will quite likely be made mostly of 3,000 Line, 50/50 Carbon Fiber/Kevlar with some 1,000 Line where necessary ... Target weight(s): 350 #'s for the hull and 150 #'s for the Capsule ... Total Target Bare Hull & Rigged Capsule ... 500 to 525 #'s.

[ONAROLL]

Contact OkieDave here on the boards, he uses a stepped hull design in the tunnel jet boats that he manufactures, and by personal experience they are quick.......

[glassdave]

Bear- thanks for the info. i just went to your website. cool stuff man.
OnARoll- i will see if i can contact him. thanks