I have a MBz jetsprint v1 hull https://www.offshoreelectrics.com/pr...od=mb-hull-610 and his jet unit installed in it. It runs on a 2000kv motor on 4s and for the life of me I can not get it to stop porpoising. I have tried moving the center of gravity forward, backward, trim tabs, no trim tabs, trim up, trim down and trim neutral. Then I saw that his new hull(v2), the flat portion of the hull extends to the front. So I cut my hull out and extended the flat section much farther forward and the linked video above is the result of the change. Slightly better than it was but still just bouncing away. I am on the waitlist for one of Youngsta's boats and can't wait for that but in the mean time I would like to try to get this figured out. All of MB video's his boats do the same thing. Is it just a flawed hull or what can I do to get this thing to just settle down?

Thanks

Here is a pic of the inside of the hull and the back of the boat(tape is just there from moving/removing things(trim tabs and such).

Well...that is the most unusual control rod linkage I have ever seen....is there a chance that the vertical trim is moving up an down whilst running and causing the hull to porpoise?

I have been moving around the position of it so it has gotten a little mangled in the process. By design the trim adjustment was on the side but it was pushing on one side as it was connected there and then causing the plastic to crack so I just centered it in the middle which gave me even pressure on both sides. I was thinking of not using a servo for it to be adjustable and just using something like this https://www.aliexpress.com/item/6pcs...508.4.8.HWu6qI to fix it but still have some adjustability.

I need a new pushrod but the LHS here closed. Takes a bit to get a new one in. It is holding it steady though with throttle applied.

It is going to take a combination of things to tame that hull. Disable the nozzle trim - set the nozzle flat parallel to the bottom of the hull, then tighten the trim ring hinge screws all the way and CA glue it that way so it can't move. Put the trim tabs back on making sure they are 1mm above the bottom of the hull (these cannot be the cheap, flexible tabs but solid). Install a 60mm ride or 'cav' plate under the jet (Kayaker on this forum has a good design) this cannot be flexible - if so, bend 5-10mm of the sides up for stiffness. Then put your battery in front of the motor. If it tries to porpoise move the battery forward a little at a time until it stops. Or slow down. Mickie never got his to stop hopping but it can be done. Not the best hull design, I'm not a fan of flat keels or tilted jet drives.

Does it matter how far past the end of the jet the cav plate goes?

60mm should make it even with the end of the jet. You don't need it any longer.

Im not surprised it propoises, there are no lifting strakes under the bow of the hull . They just stop short...

Originally Posted by sundogz

Mickie never got his to stop hopping but it can be done. Not the best hull design, I'm not a fan of flat keels...

You may be thinking of one of his many prototypes. This one works well.

For my style of jet boating in rapids, Mickie Beez hull is one of the best. I have been waiting for an ABS version to replace my very fragile glass one. I'm about ready to give up and copy his basic shape in Kevlar and epoxy for my own use. In rapids I don't want chines in the front half or strakes at all. I'll reduce the V in the bow a little and make a mold with these few changes. Of course I'll add my up-side-down fins (ride plate) to get great steering control and very little porpoising.

Here is a photo of one of my ride plates. If playing in rocky rapids make them strong.

You are no doubt right there. But we never saw his boats being used in their 'elements. It was always hopping along on a pond or lake or what have you. He would have done much better to market them for your purpose - rapids and frothy water.

I remember asking him to make a 1:6 scale Jet Sprint, because you had so many accessories you could peddle to. Barbie and G.I. Joe were 1:6. There are a lot of 'heads' and fake motors and such that would keep the masses busy with accessorizing. But that is a lake boat, not for whitewater. And that never came to fruition either. Shame.

Thanks for the suggestions guys. I have some material for a ride plate. Hopefully I can get it cut and secured for a trial this weekend.

Ride plate made a huge difference. Thanks for the tips Kayaker and sundogz. I think I can work out the last little bit of porpoising with adjusting the cog with the battery.

Good to hear it.

Here's a different way of looking at porpoising.

I picked up a garden hose with a nozzle on it about 1 meter (3 feet) back from the end. I shook it back and forth. The water velocity whipped it even more. I got to thinking this was like my boat porpoising. I think that with a jet nozzle that has a trim servo a person could add a gyro to counter the porpoising.

Food for thought?

Originally Posted by Kayaker

Here's a different way of looking at porpoising.

I picked up a garden hose with a nozzle on it about 1 meter (3 feet) back from the end. I shook it back and forth. The water velocity whipped it even more. I got to thinking this was like my boat porpoising. I think that with a jet nozzle that has a trim servo a person could add a gyro to counter the porpoising. Food for thought?

That would be an interesting experiment, to be sure. But if having it trimmed down all the way doesn't 'control' the hopping, I don't see how having it switch (quickly) between up and down will do it. It'd still be an interesting experiment. Gyro's come fairly cheap nowadays and plug right into the receiver. And they're quick enough to control a heli, so that's saying something.