Roca Speed rails & what it will take to see 80 mph
 

I am still thinking about getting speed rails. It is about the only thing left I can do to the boat to get more out of it aside from a drive extension and more HP.

Has anyone priced them out. this would be for a 28ft single engine Scarab

The boat is currently doing 74 - 75mph. I haven't dialed it in yet to see if I can get more out of it and the prop still has to labed. But before I send the prop out i am going to try a 1.36 ratio drive. i was told I might get a one or two mph out of it with my application.

anyone have an Idea of what kind of speed gains I could expect with the rails???

If I am currently doing 75 mph is it possible to see 78-80 mph with the 1.36 drive, labed prop, & speed rails????

I doubt the 1.36 drive will help in your application as it will decrease torque at the propshaft and increase propeller speed so you will need to go down in pitch. A good lab finishing is usually worth a few mph. I have not tried any speed rails, They should work however placement on the strakes is critical and may require moving them a few times to optimize the setup. Good Luck The Ironman.

please provide the following info and maybe i can shed some light on the subject.

engine rpm @ wot
prop pitch
gear ratio
present speed @ wot

see if i can help

what are speed rails? Is there a website? Anyone use them?

I don't see any advantage to going to a 1.36 ratio. So long as you are below 32" in pitch a 1.5 ratio will accelerate better.

I tried 1:36 gears in my boat, if you are not currently on the rev limiter with the largest pitch prop available, I think that you will be waisting your time.

Thanks guys for your advise . maybe I wont bother with the gear change.

mrv8outboard I am putting the boat back together after loosing a lifter and crashing a valve into the piston. I only ran the boat for 1 hour this season and I haven't gps it yet all I did was run next to my friends Skater and he said I was doing 75 . apter doing a prop calculation it worked out to be with in that range with 10 percent slip. I hope to have the true #'s after this weekend,

What I did see on my short first run was 5400-5000 rpms with a full tank of gas and a bunch a weight in tools that I was carrying with me. the prop is a 25 pitch with a 1.5 ratio . the boat is a 28 Scarab with a pad bottom. I hope this helps, Thanks

Paul

Id still like to know about these rails??

Do a search on OSO about the rails, I asked about them a while back and a lot of people had a lot of bad thing's to say about them.

Hey Paul,

Considering the size/weight of your boat, I think it is running very well. My boat is quite a bit smaller than yours, and I am only able to spin a 25 inch prop to 5300 rpm. If you want, I can bring a radar Saturday so you know for sure.

Dave