Speed predictions for twin drive boats

[keithbradley]

Ive been using the conversion tables on OSE for speed estimates of my boats for some time now, and they work well. However, there isnt anything for twin setups. Any advice? I was thinking maybe lower the prop slip on the regular table, but I wouldnt know how much...

[jac4412]

Well a twin setup won't get you that much more speed, just more pickup and raw power correct? Depending on how fast your boat is going... The difference could be anywhere from a couple MPH (top speed) to something big like 10 mph. Whats the size of you boat (and setup)?

[keithbradley]

Im going to more than likely try lots of different combos before Im done, but right now its a 30" cat with twin 1520/1600kv on 6s with cr x447s

[jac4412]

Ok, and what is your estimated speed?


You should just spend 50 bucks on a GPS... make this alot easier....

[keithbradley]

Its a new build...not even finished yet. If it were I would just use my GPS but I am refering to using the table (or other calculators) as a tool to set up a boat, not estimate speed of a boat that I am already running. Youre right, I would just use my GPS for that.

[Simon.O.]

Useing my highly scientific and calibrated "eye" I can say that with the same hull the speed is a little higher on twins, not significant but still noticable.
Big bonus is the acceleration, sound and .......cool factor ! plus the ability to drive home when a shaft leaves the boat

A single setup costs less than a twin but the way I speced it I now have two well overpowered therefore understressed drivetrains and have good reliability with low temps and a bit more speed than a single.

I wanted twins because I had to have one, did I mention how great they sound and the acceleration ??

Do twins if you must, like me, but for for a SAW setup ............ask Jay.

[Rumdog]

It will be fast! That is all. Twins ARE faster. I have proof.

[forescott]

Keith, I used the OSE speed calculator and plugged in all the info for my twin cat gps'd at 61mph. Then played with the slip settings til I got the exact speed I had on gps. I ended up with 10% slip. Hope that helps!

[jac4412]

10% really? I'm at work now playing around with the calculations, I was going to suggest a greater decrease, more like 25% slippage.... I wonder why you found it to be so low? Maybe its dependent on each motor setup and not a uniform comparison on all motors? I'm a bit perplexed... 10% seems rather low. I'll have to play around.

[BakedMopar]

With twins your driving two props. Double the surface area.

[Eodman]

A couple of years ago - mid 2008 someone posted a formula for figuring out speed on twin drives! Search the older entries in either this section or the building section. I wrote it down have to look for it!

[keithbradley]

Keith, I used the OSE speed calculator and plugged in all the info for my twin cat gps'd at 61mph. Then played with the slip settings til I got the exact speed I had on gps. I ended up with 10% slip. Hope that helps!

Makes sense to me. I wonder if Rumdog's twincat would net the same results?
What kind of motors are you running and what efficiancy % did you enter?

[forescott]

The motors are 380-9xl's (2612kv) And I used the recommended efficiency of 80%.

[Eodman]

OK Keith - back on 02/22/2008 one of our members ... aka 10guage, posted a statistical formula if you search for it - it should come up, read the whole thread! When applied to my Twin Jolly it came within 2 mph of actual

The thread is titled "Formula for Calculating Speed" !

Hope this helps!

[keithbradley]

OK Keith - back on 02/22/2008 one of our members ... aka 10guage, posted a statistical formula if you search for it - it should come up, read the whole thread! When applied to my Twin Jolly it came within 2 mph of actual

The thread is titled "Formula for Calculating Speed" !

Hope this helps!

I found it, thanks for the tip! According to his formula, you would account for 12.5% slip instead of 25% slip with single prop applications. Thats consistant with what forescott was saying..at least pretty close.