Scarab Porpoising Problem

[Parker Boland]

Hello,

I have recently purchased a Scarab 165 HO Impulse and its been porpoising constantly at all speeds. The boat only has 5 hours on it and the problem has been extremely frustrating.

I know there is a break in period on the boat, but I don't see how this could be a problem. Any help would be appreciated.

Thanks

 

[Speed_Freak_039A]

I sometimes get that. It helps to just put it in a very slight turn to cut the porpoise. Not sure yet if it depends on the conditons or the riders and positions. I was thinking maybe a plate to trim the nozzle down just a hair

 

[Speedling]

Cutting to the side helps as stated.
It's a small boat so if you aren't wave jumping you will be porpoising. Put weight in the front for starters to play around with that. Since jet boats don't have a large piece of aluminum in the water to attach fins like an i/o you need to play with weight distribution.
Find someone near you on the user map that is knowledgeable to see if you can have them watch you and possibly record it.

 

[Murf'n'surf]

Unfortunately it's a small boat issue commonly solved with adding a hydrofoil to the outboard lower unit.

Once you start porpoising it will continue until you turn or slow down. I've always slowed down so the bow would cut into the water. Usually, it's started by the water conditions like boat wakes or wind. If this is enough of an issue for you, consider installing trim tabs.

 

[swatski]

I would install Smart Tabs by Nauticus. http://nauticusinc.com/smart-tabs-sx/
I am quite certain it would cure your problem.
Not very expensive ($120 or so on amazon or ebay), easy to install, and you can return them for full refund if you don't like them. The biggest risk is you would have some holes to gelcoat.

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[ScarabMike]

Install a trim ring. I believe 3 degrees may help. They make a 5 as well. Ill find out from the vendor at Greenhulk.

I didn't know you 165 guys were having this issue. Let me see what we can do. These will get the bow down into the water some. That should cure most of the proposing. Another fix is adding a top loader intake grate. It will have a small wing to push the water into the pump, and it also creates downpreassure. Not sure if they are the same as the skis.

 

[Speed_Freak_039A]

That's what I was talking about. On the skis we mount them so bring the front end up and here we could rotate it 180 and bring the front down. Might lose a hair of speed thought. They should have put a trim on these just like the skis have.

https://www.4-tecperformance.com/in...ucts_id=1313&zenid=6auo9gi59dm49jqqi9if1omhe1

Just not sure our scarab pump diameter. Pretty sure it's the same as the high end seadoo skis which haven't changed until these new 300s came out. Also his name is Jerry. I been a member on there awhile and have a highly modded rxp.

Maybe I can take it off my ski and try it one day.

 

[Parker Boland]

Thanks for the help everyone.

I used the boat some more today and the porpoising only happens between 5500 and around 7000 rpm. I have an former Sea Doo mechanic near by who has worked on my Sea doo Sportster before, do you know if he may be able to make an adjustment to the angle of the jet nozzle or another part of the outdrive that would have the same affect as trim tabs or top loader intake grate? With the new boat I am a little reluctant to drill into the bottom of the hull, especially because I have no experience.

Another thing that I've noticed is that the bilge pump stays on even though it is pumping no water. I don't know how to get to the floater to make sure it isn't stuck so any help with that would be much appreciated as well.

Thanks

 

[Speedling]

I have an additional wedge in my pumps to bring it up to 5 degrees on my 21 foot yamaha and it did very little. The hull really dictates the angle along with the weight placement. A wedge of 3 degrees may bring the boat up one and the jet wash up 2.

 

[Speed_Freak_039A]

In my experience bringing the bow and jet up will make it bob up and down more. You need to push the bow down and trim the pump down. I do agree weight placement and hull design and angle make a big difference also to the performance of the wedges. I know on the skis the wedge up makes 2 up riding horrible the ski will just keep bouncing but with 1 person it come out of the water more and runs great.

 

[Parker Boland]

Bringing the bow and jet up will make it bob up and down more. You need to push the bow down and trim the pump down. I do agree weight placement and hull design and angle make a big difference also to the performance of the wedges. I know on the skis the wedge up makes 2 up riding horrible the ski will just keep bouncing but with 1 person it come out of the water more and runs great.

So is it possible to trim the pump down to fix the porpoising? It seems like a pretty rigid system that would require a lot of work to adjust.

 

[Speed_Freak_039A]

The link I posted should bolt right on. Might need longer bolts. I know the kit comes with longer bolts but it's meant for the seadoo skis which dont have this bulky reverse bucket housing that bolts on. Little different design. Worse case you would need different bolts.

 

[Parker Boland]

The link I posted should bolt right on. Might need longer bolts. I know the kit comes with longer bolts but it's meant for the seadoo skis which dont have this bulky reverse bucket housing that bolts on. Little different design. Worse case you would need different bolts.

so installing these rings upside down will reverse their intended function?

 

[Parker Boland]

Install a trim ring. I believe 3 degrees may help. They make a 5 as well. Ill find out from the vendor at Greenhulk.

I didn't know you 165 guys were having this issue. Let me see what we can do. These will get the bow down into the water some. That should cure most of the proposing. Another fix is adding a top loader intake grate. It will have a small wing to push the water into the pump, and it also creates downpreassure. Not sure if they are the same as the skis.

I looked at the trim rings that @Speed_Freak_039A recommended and they are supposed to raise the bow. He recommended flipping them around, would this work or do they make rings that are made to push the bow down?

 

[swatski]

This is an interesting thread! If those trim adjustments with rings, ride plates, etc. work in a boat, I will be amazed. I played with the ride plate angles in my 190 Yamaha, complete waste of time. I know @SamCF did, too.
Don't know of any boats needing top loader intakes other than the speed jet boats with Berkeley pumps.

I still think the Nauticus tabs are the ticket here. It would make the 16fter feel like it is 19 or so, no joke. These thing just work, and were actually designed to cure porpoising in small boats.

Curious what you guys find! Subscribed.

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[Speed_Freak_039A]

I do agree the trim tabs look like the answer but nobody is going to want to drill holes IMO. Maybe I can try my wedge upside down and confirm fitment for you guys in the near future. I would think the bolt pattern is in a flippable pattern but I know on the skis we use the 2 holess on that wedge that connect to our siphon tubes. Not sure if there would be a fitment or clearance issue rotating it 180.

Only problem I thought about last night is extending the reverse and steering cable. Not sure if there is enough adjustment on the srock cables. On my ski we use a extended heim joint for steering and for trim we use a extension also.

 

[Parker Boland]

Thanks for the input and help everyone! As of right now I am leaning towards the trim tabs, but no decision has been made.

I just had a question; Is porpoising a common problem with these boats? If not what could be the problem with mine causing the porpoising?

Cheers

 

[Speedling]

Watch some jet boat rooster tails on you tube. These guys trim up like 15 degrees.
The boat hardly moves other than slow speeds and take offs because of it.

Trim tabs only bring the bow down but that is what you need if you are porpoising.
Check it by loading all your weight/people in the front. This will start to do the same thing as trim tabs.

 

[ALAN MANN SR.]

I have a 165 Ho no tower, and only will start porpoising at 30 MPH. I will speed up or slow down a little to stop it. I have no problem at 25 MPH or 35 MPH. I think the tower on that small a boat is no advantage or has no purpose at all and may cause the problem. Trim tab , or any thing that would put the bow down would only be good on smooth water. On any chop it would make the bow go under. River or in land is 25 MPH or idle, Tampa bay is what ever you want to do so porpoising in chopy water is no problem. I am not sure if adjustable trim in the nozzle would make any difference. My two cents only.

 

[Speedling]

Trim does so little on a jet.
Watch this video. How high do you think he has it trimmed? How much did it effect the bow up or down?