A little different Stroker build

Eddie, PLEASE buy this prop! Brand new Acme 431 on ebay for $235 shipped... smoking deal!

Acme 431

backfoot100 wrote: The cavitation plate is actually more of a trim tab than anything else. It would be very easy to remove this for that little extra that all the speed demons are looking for ..

I would highly recommend not even trying doing that, not even once just to see the results... it may also function as trim tab and rooster tail shaper but it definitely also serves as a cavitation plate. The rudder extends well beyond the back of the boat and between that and it's relatively thick foil-like cross section it will very likely pull in air intermittantly at high speeds without that plate. That would result in intermittant inability to steer at high speeds, which I can from experience tell you is pretty much undesirable. Now, would I possibly play with a couple spacer washers on the front to level it out a bit....

Here is some interesting info.

I have been asked numerous times what the cavitation plate on the transom is for and if it's specific to the Barefoot Skier. I have always originally thought that the Barefoot model specifically had the plate well before Scarpa made it so popular but I have since found out that all AmSkiers have the plate.
After talking with Boat Doc and reading numerous posts about hull hook, I decided to break out the level and take a few pics.
As you can see, there is virtually no power robbing hook in my hull that is common place in the CC's.
The cavitation plate is actually more of a trim tab than anything else. It would be very easy to remove this for that little extra that all the speed demons are looking for without touching a belt sander and totally destroying the hull, gelcote and wake characteristics that make this a ski boat.
I can already see Reid, Tim and Joe calling dibs on who gets the next AmSkier that comes up for sale. They don't come along near as often as a CC does.

From the forward most portion of the base plate


From the end of the transom


From the end of the plate itself.


The angle of the plate in relation to the hull.

backfoot100 wrote: Thanks Tom, Yeah, it would be really interesting to get a new 13x14 federal and see what that prop does. That was my reasoning in trying the 13x14 Legend. My only dis on the stock prop is that it does have a lot of turbulence in the wake and the aforementioned slipping. Makes barefoot wake crosses difficult but not impossible. The Force and XMP both had distinctly smaller and smoother rooster tails observed from the boat. I would assume that would translate to a smoother wake table for crosses but have not been able to verify. My daughter and I did do some slalom runs with the Force and the Legend. We both ski at 15 off which puts the rooster tail about 3 feet in front of the ski. Both of us noticed a smoother crossing so I have to assume barefoot crosses would be smoother also. It may just be the rebuilt prop creating the turbulence. Like I said, a new 13x14 federal would be an interesting try.

I think we are on the same page. I'm a slalom junkie too. I run the 4-force 13x13, and the wake is the best of the bunch, the roost wash is markedly low, flat and wide , vs narrow and high with the acme's i've tried.
However, it feels that if I worked the engine over to push 5krpm or more, there would be too much parasitics vs other designs to see superior speed with the force.
If the 4-force didn't exist, the federal would be on. The federal had some marginally superior wake charateristics at 28-30 mph for the family, but I like 34-36 and that was where the force really shines.
I also like how it launches, the revs fome up faster then it digs pulls hard. The force could make things a little frothy in the table above 40, I never foot behind my boat, and when i did it was a friends 2001 or sanger

GottaSki wrote: Excelent build, well done. Lot of people crap on it, but I found a late-model Federal to be a very good prop on my supreme, which is not not a distant stretch from your hull. Had superior efficiency, wake, and roost characteristics to many more exspensive, modern props.

Thanks Tom,
Yeah, it would be really interesting to get a new 13x14 federal and see what that prop does. That was my reasoning in trying the 13x14 Legend. My only dis on the stock prop is that it does have a lot of turbulence in the wake and the aforementioned slipping. Makes barefoot wake crosses difficult but not impossible. The Force and XMP both had distinctly smaller and smoother rooster tails observed from the boat. I would assume that would translate to a smoother wake table for crosses but have not been able to verify.
My daughter and I did do some slalom runs with the Force and the Legend. We both ski at 15 off which puts the rooster tail about 3 feet in front of the ski. Both of us noticed a smoother crossing so I have to assume barefoot crosses would be smoother also. It may just be the rebuilt prop creating the turbulence. Like I said, a new 13x14 federal would be an interesting try.

A little late now but as you experiment take note of prop to hub, prop to rudder and prop to hull clearance, some feedback there would be good to know. Any ill handling from any of the props at speed? I assume you boat has tracking fins?

Joe,
Thanks for the feedback. My eyes have been opened quite a bit so far. I keep thinking why wouldn't more guys want to take out cup and add pitch. If the engine has the torque to spin it you would think that you'd get more overall performance. When you talk with prop guys, they insist that you need the cup or the boat shakes itself apart. I have to disagree at this point but I'm far from expert at this stage in my testing. FWIW, my stock prop slips and shudders horribly when you get on it but it's still the fastest prop to date. It immediately spins up to 5K+ RPM, shudders a little bit and starts to walk a little bit to the right but it still tries to pull. Virtually all of the other props tested (except the cupped Force) pull hard with very little slip but fall short on WOT MPH.
I'll take your prop along for the AmSkier reunion and let some guys try it out with their stock motors. I'll bet there are more than one who will want to keep it. If you do want to sell it, let me know what you want for it and I'll keep you posted.

Brian and Alan,
I've heard several reports just like yours and I keep expecting those same kind of results but so far have been very disappointed. The XMP has so far been the most positive. Like Alan stated, that prop pulled really hard all the way through the RPM range like a sports car but just didn't have the WOT MPH. I keep expecting that magic bullet that gives me 57MPH like you talk about. I don't know if my expectations are too high or just haven't found the magic bullet yet. It's been a learning experience for sure.

Dave,
My ears were ringing that weekend. I had a feeling there were some very heated discussions going on.

hotboat wrote: Very similar to my experience as well, with the 540 I was 5800ish and 54-55 mph and after going to th 13x13 acme 430? i think (same as Alan) went to 5200-5400 and 57-58 mph

I would have to agree with this entirely, the 541/540 lets the motor run away with no gain but the 430/431 prop is the ticket. Brings the rpm down and in my case gained slightly on mph but most of all felt like a sports car through the entire rpm range. Very grippy and responsive, never felt like it was losing any bite no matter how hard you mashed the throttle.

Very similar to my experience as well, with the 540 I was 5800ish and 54-55 mph and after going to th 13x13 acme 430? i think (same as Alan) went to 5200-5400 and 57-58 mph

Sorry about the delay here Joe. I missed this post for some reason and I don't know how.

I have had a chance to run it and test some props. So far they've been less than hoped for but still working with OJ to try different flavors.

Here's where I'm at so far:
All of the speeds are GPS results.

Stock Federal 13x12 that has been rebuilt and repitched to 13x13
55MPH @ 5800RPM

OJ XMP CNC 13x12.5
Uncupped   52MPH @ 5900RPM
Cupped     53MPH @ 5500RPM

OJ Force 13x14
uncupped   53MPH @ 5700RPM
cupped     50MPH @ 5300RPM

OJ Legend 13x14
cupped   51MPH @ 5100RPM

Acme 13x12 CNC (Joe's Prop)
53MPH @ 5900RPM

It's pretty amazing what cup does to the results. Much less RPM and MPH except for the XMP. It gained a MPH while losing 400RPM. They've all had good to impressive holeshots and pulled well all the way through WOT. The only one that really sucked was the Force after it got cupped. That lost a lot through the entire RPM range.
John wasn't available while testing most of them to feel what differences they had while pulling a skier or doing wake crosses. That would have been really interesting. So I really only have top speed and RPM numbers to go by right now. All of them have had no felt vibration at all.

Overall, I've been less than impresssed when you talk about top speed numbers vs. the stock prop. I just think that I should be able to find something that shuold do 55MPH at someplace around 5400-5500RPM. Maybe my expectations are too high. I don't know. The XMP was good and pulled really hard but still a couple MPH short. The Force set some really high expectations to start but after getting cupped, fell flat on its face.

I'm currently waiting for a lesser cupped Legend to be sent back to me. So that's where I'm at to date.

FYI, I'm going to an American Skier reunion in June and if you're interested, I'll take that Acme prop of yours along and I'd probably be able to sell it for you. I know you said it has just been collecting dust in your shop. I can either send it back to you or if you want me to try and sell it, let me know how much you want for it and I'll see what I can do. Thanks so much either way for letting me try it out.

As always, I welcome any input that you might have.

Hollywood wrote: 300hp DXII seemed to like the 13x12 Acme. Joe, still kicking that 431 around?

Sadly no, at least not in usable condition.   I bent that one worse than any prop I have ever seen.   I do have a 541 in good shape though - be happy to bring it to the river run if he can wait that long

300hp DXII seemed to like the 13x12 Acme.

Joe, still kicking that 431 around?

Eddie, the description sounds great- cant wait to see the pics (theyre not visible here at work).

As far as props go, I dont think Id spend a dime having a prop repitched. Its just going to fatigue the metal and increase your chances of flexing the blades at higher RPM. Best case, that doesnt happen- but youre still running an old-school hand finished prop. I think you'd be worlds happier with a modern CNC prop (Acme or OJ XMP). Exactly what size works best will depend on where youre making your peak power- have you plugged your numbers into some dyno software to see where that may be? For reference, the 383ci Response Barefooters come with 13x13 Acme's, so that might be a good starting point.

Ive struggled against motorbox height on a few different boats. Whats your plan for raising it up? I raised the box on our BFN by adding more glass to the bottom lip of the box. I went the other route on my '90 and reduced the height of the engine with a lower profile arrestor. Eliminating the carb spacer is another option. A 2" tall arrestor might prevent you from having to build a stand for the box though- you can find them out there if you look. If I remember correctly, the K&N's were close to 4" tall when I was looking a few years ago.

very cool! I like that K&N flame arrestor too, really tops it off. The lid still wont go down even with that on there? I thought it was lower than the stock one.

That engine looks awesome. Nice job. I hope it runs as good as it looks.