Gear Ratios for Speedmaster #3's

Pash 1 · 05-04-2009, 09:27 AM

Have been reading on the USA sites that most speedmaster #3's are running a 33/1 ratio on them - whats the advantage over the 1/1 ratio's we have in D2S ?

Tony Davis · 05-04-2009, 10:02 AM

I think you mean 1.33:1, and the question ought to be "whats the disadvantage of running 1:1 ?"

Jon Fuller · 05-04-2009, 10:18 AM

You might have trouble finding 15" pitch cleavers!

Pash 1 · 05-04-2009, 10:54 AM

Quote:

Originally Posted by Tony Davis

I think you mean 1.33:1, and the question ought to be "whats the disadvantage of running 1:1 ?"

Yes Tony as always you are right - So for the sake of Clarity " whats the disadvantage of running 1:1"?

Quote:

Originally Posted by Jon Fuller

You might have trouble finding 15" pitch
cleavers!

Im having trouble finding any Cleavers at a reasonable price got the 16 1/2 inch 26P ones but thats all

But I understand that Petrol has a torque at low revs and she would be forever getting on the plane is this true therefore would the 1:33:1 BE BETTER? OR MAKE IS WORSE??

Tony Davis · 05-04-2009, 11:15 AM

I wouldn't worry too much at this stage about torque or which ratio would be quickest etc. The important thing is to find a ratio that best suits the props that are available, that on paper will give you the speed the you expect the boat to obtain.

I think from memory, the ratio's available for you drives are 1:1, 1.18:1, 1.25:1, 1.33:1, 1.40:1 and 1.5:1. I've always thought 1.5:1 is considered to be a "petrol" ratio, for an application such as yours.

The theoretical max speed with this ratio and your drives, motors turning 5000 rpm would be 82mph, so with prop slip of 10% youd get 74mph. It's not an exact science, but it's a good start.

1:1 would give 123mph!!!!!!

I seem to remember talking to you about this several months ago.

Pash 1 · 05-04-2009, 12:09 PM

Tony your recolection is correct my grey cells seem to be wearing out faster than yours (must be a cake thing) John Hedges calculated a speed of 82mph when he did the maths but cant remember what ratio he used. So 1:1 not a good Idea based on your calcs and 1.5:1 better than 1.33:1 then yes

Jim Brooker · 05-04-2009, 02:44 PM

Quote:

Originally Posted by Pash 1

Tony your recolection is correct my grey cells seem to be wearing out faster than yours (must be a cake thing) John Hedges calculated a speed of 82mph when he did the maths but cant remember what ratio he used. So 1:1 not a good Idea based on your calcs and 1.5:1 better than 1.33:1 then yes

Martin, When I run the boat as Macho and Ballerina it had 600bhp Westlakes petrol engines the max speed was 82mph on 1.33:1 drives and 26 or 27x16.1/2 short hub props.
And when I run it as D2S,Follett and Rejuga with the 600bhp Sabre's the max speed 82mph on 1.1 drives and the same size props, on the Sabre's there was a stepup box, to get the prop into 2300 to 3000 rpm
Now it would a little better with 1.40:1 or 1.50:1 drives with long hub props depending on your engine power.
Martin are the drives still 21ins apart, it would be better if the drive were back to 18ins apart.
Hope this all helps ????

BluFin · 05-04-2009, 03:45 PM

Quote:

Originally Posted by Pash 1

John Hedges calculated a speed of 82mph when he did the maths.

Quote:

Originally Posted by Jim Brooker

Martin, When I run the boat as Macho and Ballerina it had 600bhp Westlakes petrol engines the max speed was 82mph ?

Well I guess the Maths works

Pash 1 · 05-04-2009, 05:02 PM

Jimmy the simple answer to the question of spacing is "I dont know" was down at the boat today an should have read your post before going there, Ive got the offer of a pair of 17 1/2 28P long hub cleavers in the states and their not that expensive around £800 for the pair is it worth going for them?

Jon Fuller · 05-04-2009, 05:17 PM

Assuming your motors do make circa 600 horses, and that they turn IRO 5200rpm (to be honest, if they're really 600+'s, I'd expect them to rev higher, maybe 5500, which will make things worse) and you stick with your diesel ratios (Assuming 1.1:1) you're going to need props of around 19-20" of pitch (which you won't find, coz if they do exist, they'll be as rare as rockin horse shit) If you find yourself some 1.5:1 drives, or similar, or re-ratio yours, you'll need circa 26-28" pitch props.

Pash 1 · 05-04-2009, 06:06 PM

Quote:

Originally Posted by Jon Fuller

or re-ratio yours, you'll need circa 26-28" pitch props.

Thats exactly what im thinking of doing Jon re-ratio to 1.33:1 or 1.5:1

Jon Fuller · 05-04-2009, 06:23 PM

1.33:1 might be a bit tall. if the motors are short on power (vs your hopes) the props you have will be too tall/long. if the motors are more like 500-550, and rev to 5200, on 1.33:1 you'll need 24's. so you'll be doing ratios & props.
If you re-ratio, I would play safe and go 1.5:1. But, rebuilding/re-ratio-ing SSM's isn't childs play, you'll need to find someone with the knowledge and skill, & the special tools, otherwise you'll be doing it more than once (rebuilding)

Pash 1 · 05-04-2009, 06:26 PM

Quote:

Originally Posted by Jon Fuller

1.33:1 might be a bit tall. if the motors are short on power (vs your hopes) the props you have will be too tall/long. if the motors are more like 500-550, and rev to 5200, on 1.33:1 you'll need 24's. so you'll be doing ratios & props.
If you re-ratio, I would play safe and go 1.5:1

Thanks Jon I'll go for the "Safe" option what do you recon about the props from the states as I said ive got 16 1/2 25's what do you think about 17 1/2 28's long hubs to big?

Edit: In answer to your Edit Jon yep your right I will find someone (dont know where from - but I will)

Jon Fuller · 05-04-2009, 06:32 PM

I'm not sure on the diameter. unless I had cash to burn, I'd get the motors in, get the drives re-ratiod, and try your 16/12 x 25's. then go from there.

I'm sure Jim B could give better advice on diameter, but would think he'll agree on revs, ratio and pitch (and the unknown power)

Pash 1 · 05-04-2009, 06:34 PM

Quote:

Originally Posted by Jon Fuller

I'm not sure on the diameter. unless I had cash to burn, I'd get the motors in, get the drives re-ratiod, and try your 16/12 x 25's. then go from there.

Advice noted and taken

Tony Davis · 05-04-2009, 06:44 PM

I'd be buying 2nd hand drives in the correct ratio, a set of 1.5:1 gears retail at £4143.63 + vat, but i could let you have a bit of discount.

Pash 1 · 05-04-2009, 06:55 PM

Quote:

Originally Posted by Tony Davis

I'd be buying 2nd hand drives in the correct ratio, a set of 1.5:1 gears retail at £4143.63 + vat, but i could let you have a bit of discount.

Tony Davis · 05-04-2009, 07:06 PM

http://www.speedmasters-inc.com/

Brand New! SSM III upper complete. 1.5 ratio. $3500.00

BluFin · 05-04-2009, 10:28 PM

http://www.offshoreonly.com/classifi...o26935-en.html

Jim Brooker · 06-04-2009, 08:59 AM

I see all the information you are getting, but to start with are you going for staggered engines, if so the drives must be remounted at 18ins apart and the same hight as now for MK 3, or remount the transon plates, the plates are the same for MK 3 & 4 drives, if you are going for new drives, buy Mk 4 drives 1.40:1 or 1.50:1 and set the drives high, or on box's it well run better.
It all depends on your engine power if you bhp is low 1.40:1 would be better than 1.50:1.
You must buy drives MK 3 or 4 with long shaft, I have a pair of new K 18x28. 3 blade.19 splind props you can try, when you get to that stage.
I use to rebuilded all the drives, on the diesel boats the MK 3 lasted between 3 and 7 hours, the Mk4 drive a little longer. petrols up to 600 bhp 15 to 25hours racing.
I hope this is to not to much information, if you like you can ring me or I am in the South of the Uk in April.