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New Cummins/Mercruiser Project

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Old 10-02-2008, 02:50 PM
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Originally Posted by HabanaJoe View Post
You guys push me to look up to much old stuff!!!

ParriYacht is dead on the the SH's had 17" & 16.5" dia props with the Arenson's.

I can't find a pitch number but with that 1.30 reduction you have lots of torque to start spinning a prop with. After you shift into direct?????
I talked with Rik from Arneson(I found this guy amazing ,I have another brand surface drive ,and he took the time for me like I bought one of his) a while ago about propellors for my set up,his advice was to find a prop with a diameter as big as possible something like 18 inch or 18 1/2 and as many blades as possible ...I guess I have to try what happens ,like you mentioned ,I could let a prop shop cut them down to 18inch or so if getting on plane is difficult,or I need a little more rpm,s .

I like to know what sort propellorslip numbers I can expect with a surfacedrive like I,m using ?
suppose I turn 3400 rpm at 1:1 with the 26 pitch props ,and having 10% slip ,I would go around 75 mph ...

max horsepower is at 3300,so with 10% slip would be 73,5 mph, I have no idea how much slip I,m going to see ,I mean it could be like 6-8 % ,then yes the pitch is likely to big.

These Rolla props are harder to find ,and expensive too,this set was not that bad priced ,and I thought I could always let them modified by a prop shop.

The Baja 40 has a straith hull ,no rocker /hook ,I,m going to mount the weigh as far aft as I can ,such as the fuel tank can be built smaller ,like 200 gallons instead of 300 ,and mount the tanks as far aft ,just next to the first bulkhead that separates the engine compartment ,battaries close to the transom,etc etc Rik also mentiod these type drives always tend to push up the stern ,lucky the inner strakes stop at +- 10 -12 ft from the transom,and the hull itself is not really heavy .

A.J
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Old 10-02-2008, 03:22 PM
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Rik - is a wealth of information. He has seen so many applications with surface drives it's scary!!!

As far as slip goes, you got to be under 10% with big wheels like RIK suggested turning them that slow?

The bigger diameter the prop the slower it can turn to be efficient, small props need to turn faster to keep up.

As far as weight goes, the old Buzzi boats we ran plus the SH's with the diesels where naturally stern heavy because of the weight of the engines /drives. Our fuel tanks were in front of the engines and the longer range tanks were in front of the cockpit. With the diesels side by side there was no room in the engine bay for fuel tanks.

My guess is with the added weight you need the tank in the front of the engine room like we had ours.

RIK is right they lift the stern pretty good. We ran the SH's with straight bottoms no different than your Baja and they were fine - again your building a pleasure boat, it will run good for what it is I have no doubt.

Joe Gere
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Old 10-02-2008, 03:28 PM
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Joe ,I want to show you the props I have bought ,because I could not find any info ,and have not seen this type before .
Unfortunatly I can,t post here ,and can,t post them to you direct ,could you send me your email ?
Maybe you can post the pics ,so others can tell /help identify .

A.J

Last edited by stirling; 10-02-2008 at 06:39 PM.
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Old 10-02-2008, 06:16 PM
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Quote:
Originally Posted by 7075T6 View Post
My Round Britain 2008 raceboats performance figures:
36 ft Ocke Mannerfelt-hull
2xVolvoPenta D6-435(3700rpm) and DPR-drives
GR-9 propellers modified w 31" pitch
12000 lbs dry
75 mph with 1100 liters of fuel at 3700 rpm-could use larger propellers
On the 210 nm stage from Inverness to Edinburgh I backed
of once from WOT.
We drove the boat from Sweden to Portsmouth and Round Britain. 2500 nm together.
No problems whatsoever. The engines used 2 liters of oil during the 2500nm.

www.teamvilda.se
nice pics, the water looks coooooooolllllllddddd!
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Old 10-02-2008, 06:45 PM
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[email protected]

or

[email protected]

I'll crop and post for you, no problem!
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Old 10-02-2008, 07:21 PM
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ok, dumb question. I've just never seen it...even on boats that are always staggard gas setups.

Sure would be neat to have a diesel speed boat that sounded like a loud pipe peterbilt.
My last Pete had a 600 Cat with 6" straights. Would come home on the weekends to twin 600's with dry pipes in my KV.
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Old 10-02-2008, 09:14 PM
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scarab kv - that's funny!
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Old 10-03-2008, 07:14 AM
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Here are sterling's props
Attached Thumbnails
New Cummins/Mercruiser Project-018-kopie-2-.jpg   New Cummins/Mercruiser Project-019-kopie-2-.jpg   New Cummins/Mercruiser Project-021.jpg  

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Old 10-03-2008, 07:34 AM
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Bronze props will be easier to work than stainless for sure. With the size of those blades, your slip numbers should be wery low and getting on plane shouldn't be a problem either. Looks like a well thought out project. Good luck. Bam has a couple of formulas for hp to speed and prop slip you might want to look at. http://www.go-fast.com/bam_marine_knowledge_base.htm
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Old 10-03-2008, 12:25 PM
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We keep trashing the same stuff over & over. The Cummins 5.9L is a great engine. But we keep overlooking it's one obvious shortfall... "5.9L"! We compare it to gasoline engines with 1-1/2 times the displacement. It's the old rule displacement = more horsepower & torque. Dang ya'all are using over 8L displacement gasoline engines why not get into the over 8L diesels. A Cummins 8.3L will give ya 600 hp without exceeding the warranty. Ya'all scream about the weight but if you were to change some of the hull parameters to work with the extra pounds you can make it work. Also when you start down that path why half step? Try jumping up the 11L to 14L class engines. There are a bunch of good engines in that range. CAT C-15 ACERT, Komatsu 6M140A5 and a bunch of euro engines. I've seen a lot of patrol boats in the 40 ft class that cruise all day long at 50 to 60 knots and when you throw the sticks to the wall will squeeze out a tad over 70 knots. They are all running close to 14L displacement. It all boils down to engines and tatas bigger is better!
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