Help with prop selection, 55" Dumas Wellcraft Scarab 380

Rickracer · #1 01-15-2005, 11:48 PM

Brand new Homie, no mods except gutted and piped stock muffler and big bore carb. I have been running a Prather 260 (SS). I have the following props at my disposal:
Octura X448, X452, X455, and X465, 1450, 1455, 1457, 1460, 2.1/3, X447 (3 blade), X460 (3 blade); Prather 260 (SS), and last but not least, a Prather 270. I have played with propshaft height and angle a bit but I can't seem to get much lift. The height and trim is now where it will cavitate if it turn it too aggressively, but hooks right back up coming out of the turn. The hull rides very wet, and the motor doesn't seem to be peaking. I've tried adjusting the needles, I can get it to what seems optimum, and poorer on both side of that, but it still doesn't sound right. Am I running too much prop? Will a header and chamber make an appreciable difference? Or do I just need more power for this amount of weight?

Doubledog · #2 01-16-2005, 01:52 AM

Rick, are you running a 1/4" shaft? If so, the only prop you've got that would come close to working is the Prather 270. For the Homie, you're going to need an Octura X470,
x472
prather 275
Prather 280

could even try an octura x470-3 blade. If the engine is not swinging the 270, then something isn't right. Is it a surface drive? Drive coming out the bottom of the transom, not under the boat?

Rickracer · #3 01-16-2005, 02:51 AM

Yes, It's a 1/4" shaft. Here's some pics of the boat. I have more and better ones, but no way to get them out of the camera at the moment.

Rickracer · #4 01-16-2005, 02:56 AM

If I can find a couple more pieces, I'll have enough to do a strut & rudder setup on the used cat hull I bought at the WinterNats today.

Doubledog · #5 01-16-2005, 03:01 AM

like this?

If so, its sub-surface drive. Makes for harder prop selection.
Not bad, but the surface setup is better.
Does the word SATAN come to mind? Lmao !

.

Doubledog · #6 01-16-2005, 03:04 AM

The only thing I recognize is the trim tabs. Need a side shot of the gear if possible. Btw, the turn fin.... move it to the chine but keep the 90* angle w/the bottom of the boat.

Rickracer · #7 01-16-2005, 03:16 AM

The 260 is the one on the right. Does it look like it's been worked? I don't know if you can tell from the pic, but the 260 is stainless, and is about 1/4" smaller in diameter. If the 270 would be better, I'll try that one.

Rickracer · #8 01-16-2005, 03:34 AM

My scanner isn't the best thing to use for this. I was a little nervous about setting the boat on the scanner.

Rickracer · #9 01-16-2005, 03:42 AM

Once it's dialed in, I'm gonna teach myself to paint

Doubledog · #10 01-16-2005, 03:51 AM

Pics are getting better

Neither prop has been worked.

1/4" prather props start at the 270 range. Don't see how you could get the 260 to fit on the shaft. Just that ones got a bushing slid in.

Your boat looks to be an older style sub surf.

I'm lazy man. Sell the engine for $50 & put it towards a Zeni. You know the aircooled 230RC Zen is running for $150 or less "NEW" on ebay ! Its putting out 3 hp stock. (funny, now that I go to ebay to post a link for one, they're all gone. I know for a fact that I've seen them for that price new.) Or you can even consider a SIKK engine. Thats where the real power for the $' is at. Talk about cheap.

Change the drive to surface & roll with it. Check out a thread I did about the Project Prather & you'll see how easy it is. You've done real boat work work... this is cake.

Rickracer · #11 01-16-2005, 10:54 AM

....if the 260 is a 3/16" hub prop, I'll bet somebody drilled it out. If you look at the two side by side above, the pic tells the story.

That 260 was on this hull when I got it, hooked up to the K&B 11cc. I cleaned up and polished the 270, and I'm gonna run it later today (after we come back from the WinterNats) and see how it works.

Rickracer · #12 01-16-2005, 07:27 PM

I bet the boat picked up 5 mph, I'd guess between 25 and 30 now. You could even see the hull torque roll when stabbing the throttle now. A little more power and I'll be cooking with gas

. Guess I'm gonna have to snag a couple more props too. After all more is better, right? Has anybody ever put a pad on a Mono? I am considering it. When I did the hull blueprint on my Glastron, I wanted to do a pad, but everybody said no, then I wound up wishing I had.

Picked up some more parts for the used AeroMarine Sprint Cat I bought at the Winternats yesterday too.

Doubledog · #13 01-17-2005, 03:55 AM

Rick, I've thought about doing the ride pad to my G'. Making it nice & large so it would fly the bow type of running. After reading several replies towards a post, I'm staying away. Some had said they'd done the same thing & it takes away from rough water handling.. & there was no real speed increase. Take for example the SAW rigs... Straight AWay boats. They're V' w/no pads.

Though there's no pad, the large rudder gives them good handling while still running loose. Not exactly the responses hoped for but enough to calm down the excitement.

kevin28 · #14 01-17-2005, 10:27 AM

Dumas uses a 1/4" cable but steps the shaft down to 3/16".

Doubledog · #15 01-17-2005, 10:47 AM

No kidding. Can see as to why they'd need to do it now with the older hulls.

Rickracer · #16 01-17-2005, 07:42 PM

And I'm pretty sure now that they drilled out that P260 to fit the 1/4" shaft. (See pic above, and look at the difference in the hub size vs. the shaft hole)