Offshoreonly.com - which props for 38 scarab flat deck

Offshoreonly.com (https://www.offshoreonly.com/forums/)

- Prop Talk (https://www.offshoreonly.com/forums/prop-talk-165/)

- - which props for 38 scarab flat deck (https://www.offshoreonly.com/forums/prop-talk/176410-props-38-scarab-flat-deck.html)

which props for 38 scarab flat deck

Quote:

Originally Posted by kvscarab38 (Post 2385549)

I have a 38 scarab kv with ssm IV drives with 2" spacer and a 18x29 4 blade cleaver prop with about 550hp it seems like it takes forever to get on plane about 30mph do i have too big of prop not enough hp not enough k plane 380 or too deep in water or just dont know how to drive once boat is on plane it runs great just maybe not fast enough 65@5000. To get on plane just set rpm at about 3000 kplanes and drives down and wait for props to hook up.
Ps straight bottom hull.
engine originally was 1987 575 hpmercury racing but has been rebuilt with hydraulic roller cam do not know which cam it has was just guessing on hp. Its a 540 tall deck with team g intake and dominator carb. Its supposed to be original except for full roller hydraulic cam set up.
and i'm not sure on x dimension also has stelling extension boxes and headers

thought i would see if anyone else has anything similar and what props you are using.thanks for all info.

Ruducing the propelller diameter 1/2" should help the cause.

Quote:

Originally Posted by bbladesprops (Post 2391533)

Ruducing the propelller diameter 1/2" should help the cause.

ok bret is that a big job to reduce the diameter or would u try different props??

i have a 1982 38 kv scarab. 572 tall decks ,dyno'd shows 630 hp at 5300 with flat tappet cam.( im turning labbed 15 1/4 x 25) to set the boat up rite you should pull a motor and get it on a dyno. it will tell you your peak hp rpms. you want to hit that rpm wfo nothing less and nothing more. its better for the motors and you get to sqweeze every mph out you can get. these scarabs straight bottoms are heavy boats, hence a light boat might turn a 30" prop with your power and a heavy boat might only turn 25" prop. my guess is -your props are way to big. with a hydrolic roller cam you should be turning at least 5500 rpm. but i would get that checked. by the way your boat looks SWEAT.

Reducing diameter is a sizable job if done correctly. It is easy to lop off a 1/2". However, the correct process involves matching the the blade area to the new diameter. Also the thicknesses need to be adjusted when the diameter is reduced. We have the ability toi do these adjustments.

My suggestion to reduce diameter is focused on the planing issues. Diameter reductions will increase rpm and will change boat attitude. I believe it will help in your situation.

Ultimately the previous poster is correct in that you need to also know the best rpm for your engine HP operation. if it is low 5000's, reduce the diameter 1/2" and then learn from the results.

Hi Bret, I have the boat in question in my shop right now and am doing all the work for Bob (kvscarab38). I have a set of 26 inch Merc Racing 5 blades that have been cut down a bit (to 16 an 1/4 or 1/2 i think) they were off #6's so i will need to get a spacer but we were going to try them in the spring. would these be a good prop for this boat? our plan is to do some testing with spacers and props in the spring to get some baseline numbers than tune from there. Thanks for your input

Pitch is inconsequential unless you know the ratios in those SSM IV's

oops . . . . forgot that tidbit of info. i will check them on monday :D

Hi Dave,

I think the first set of props are 18x29's and your props you said are 16.5ishx26. There is a large difference between the two. The small diameter will teach you something as far as planing but the 3" pitch difference also comes into the equation. The best advice would be to try everything you have available (carefully) and write down the results. With reading between the lines, we can head in the correct direction.