Skat Trak dual impeller for 1.8l engine pump

[swatski]

Interesting post by Capnkev767 on the other site describing his new Skat Trak dual impeller use in a 240:

http://yamahajetboaters.com/forum/viewtopic.php?f=242&t=67074&p=542238#p542238

Wondering if any members here have an opinion or first hand experience. Seems like a no-brainer for wakesurfing, but may also cure some of the vibration/noise issues at cruising RPMs.

From his description it reminds me of the effects of switching a 3-blade to a 4-blade SS prop in an outboard. I did it once with my 115hp rude and never went back.

 

[Ronnie]

I believe @cybuch use one in his boat for his flyboard business which is the application it was designed for. Keep in mind that per capnkev (who is not a member here) he lost a few mph on the top end of his 240 but improved his acceleration. Also he can't get up to full rpm with these impellers.

 

[robert843]

These are designed for a purpose more like @Ronnie mentioned. They are usually used in sub 200 hp water craft to help generate enough power to launch a fly board or similar product. I would probably not make switch to this product unless you do a lot of tow sports and just really are not happy with they way you boat pulls. You would definantly loose top speed with this product.

 

[swatski]

You guys are correct about the top end speed lost - it is to be expected with the dual impellers. That said, capnkev has not yet tested the top end, I will be looking forward to his full report.

(I also must admit to a hefty dose of fascination with that prop, that thing just looks bad a$$!)

What I have learned in my brief YJB ownership so far:

1. With direct drive and no gear reduction, it is all about the RPMs and the pump efficiency with these boats.

2. In its stock configuration (with a "ribbon delete" as the only engine mod) my boat's speed is limited, at least in part, by the rev limiter.

3. Remapping the ECU may help with 2, before hitting the limits of pump efficiency by other factors. If done sensibly, ECU remap/rev limit increase could be useful.

4. Cavitation is robbing a lot of power down at the low end (low speed range).
- that low end cavitation can be remedied by pump "blueprinting" (basically - keeping debris out, surfaces smooth, tolerances minimal, etc.)
- in my case, custom repitched Solas by Impros helped A LOT to eliminate low end cavitation and vibration while still allowing to reach the rev limit with minimal top end speed loss

So, with regards to the Flyboard impellers, could increased pump loading (or whatever the mechanism is with these duo-impellers reducing cavitation) lead to improved pump efficiency?
If that is the case, I don't see why one would necessarily suffer unbearable speed losses. Not to mention, there is a lot of benefits to be able to generate a ton of thrust at low ends.

 

[robert843]

I have looked around and cant find any real stats on it. I have seen people comment on it most said it wasnt worth it but then back it up with no actual stats as to why it wasn't worth it lol. All said it had better hook up but you lost some top end speed but none said how much. I have to imagine if you were doing a lot of tow sports with little top speed runs involved it may be a good up grade.

 

[Big Shasta]

That site is dead to me. So I google imaged it. Looks cool, that's for sure.

 

[Julian]

Here is the thread @cybuch posted about adding these...he said he lost about 5mph on the top end....

https://jetboaters.net/threads/dual-impellers-are-in.1853/#post-30277

 

[cybuch]

I wouldn't recommend going to dual impellers, unless you are flyboarding. You lose a lot of top end, so much that I am only running one in my setup, I started with 2. When we are in boat mode I lose about 5mph on the top end and I don't feel like its quicker out of the hole. The purpose for the duals is to pre-load the pump with water while you are not really moving forward to force water into the pump. It works great for flyobarding, but i I could find a way to switch out while on the water, I would switch back to my SS when we are towing or surfing. I hope this helps. And yes, it does look bad ass!

 

[swatski]

Here is the thread @cybuch posted about adding these...he said he lost about 5mph on the top end....

https://jetboaters.net/threads/dual-impellers-are-in.1853/#post-30277

Thank you, Julian! I looked for it but missed it somehow...
Good info.

I think I will give it a try next season, as I am in the process of rigging the boat for wakesurfing. It will never be perfect, or even great, but that's okay.

Because of where I do most of my boating (a small river), I am basically stuck with a 190 as far as a yamaha is concerned. The great thing about it - single pump - half the cost of any mod! I boat about 10min from home on a little river called Meramec, which can be crazy shallow! I have been on the river, boating, every day the last week - and our Saint Louis area friends can probably tell you that I must be nuts. The water level is low... But, after 5 years and 4 lower units I bought the little yammy and freaking love it. These boats are really well engineered but still have a lot of potential!

 

[swatski]

I wouldn't recommend going to dual impellers, unless you are flyboarding. You lose a lot of top end, so much that I am only running one in my setup, I started with 2. When we are in boat mode I lose about 5mph on the top end and I don't feel like its quicker out of the hole. The purpose for the duals is to pre-load the pump with water while you are not really moving forward to force water into the pump. It works great for flyobarding, but i I could find a way to switch out while on the water, I would switch back to my SS when we are towing or surfing. I hope this helps. And yes, it does look bad ass!

@cybuch Just saw your post- -thank you! Hmm... maybe I will not be trying it out after all. Do you think that for a sea crossing expeditions, such as the Bimini trip, the dual prop would benefit a small boat in rough seas? Just curious, based on the capnkev amazing post on the other (dark) site cited earlier.

 

[cybuch]

No, I don't think it will help. Its really when you are WOT and not moving forward. For the money, I think you will be very disappointed, unless you get a flyboard