looking for advice to gain speed

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I have a Jarvis Newman 36, 200hp John Deere m3 6068 with twin disk 506, Dynaquad 22x20 prop. I can not afford a new or rebuilt engine right now. Looking for feedback on this set up and wondering if this is efficient and how I can gain the most speed. The engine works well and has 2200 hours. The boat is a soft top that will be used for coastal cruising. Suggestions welcome. The shaft is 1.5 in. Also what should I consider in the future for repower to reach efficient 20 knot cruise. The JD seems like a good engine? Thanks for your help.
 

John 40

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I grew up on a 36 newman with a 200 h.p. perkins. I think our cruise was about 12 knots and Wot about 17 knots. The new owner repowered with a 370 yanmar I believe. I think his cruise was only 16 or 17 knots. 20 knots might be tough to attain with that hull, great boat though.
 

Badlatitude

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You need torque to swing a wheel or RPMs to swing the wheel faster. I dont seen you gaining a ton with the current engine.


Captain Larry and his magicial calculator brain could probably give you numbers for various set ups etc. Hopefully he will find this thread!
 

eyschulman

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you would probably need 400-450hp with plenty of toqure to get 20k. Your trany and shaft may not handle that.
 
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thank you

Thanks for the feedback. Given that a new or rebuilt engine with lots more horse power is not in the cards for quite a while. Any suggestions to increase speed with modifications to the current setup like prop changes gear change? I understand john Deere is a high torque engine are their others like Sisu that I should consider in the future when I can move up? Thanks for the help.
 

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A Sisu would suit your needs, although yes, your running gear might be a bit light at 1.5 inches. Easy enough to swap out to a larger size, I'd recommend installing a new shaft tube and losing the bronze packing glands. Rails might help you out as well, and take a peek at the rudder. If your post goes through the entire blade or if it's a fiberglass rudder you are losing out a great deal as far as efficiency goes. It's like putting your hand out the window flat and into the wind, then turning it 90 degrees. Big difference and air is 800 times more fluid than water.

Also just basic loading of your vessel might help you find a little bit more speed. Lighten up the forward section as much as you can to get that bow up some, takes a tremendous amount of power to lift that bow when it is heavily laden down with items.

Double the horsepower and slightly less weight would do wonders, although it might shell out your 506 gearbox (probably) so you may consider a different gearbox. Like a ZF 286A for example.
 
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thanks first team

The rudder does have the post all the way through. It is aluminum. Thanks. We also have keel coolers. We are working on taking as much weight from the bow and moving fuel from below the bridge deck to below the cockpit. The hull has a slight build up of material along the bottom at the stern. Almost like tying the heavy rope around the stern. When I can increase power shaft and gear what is your opinion of larger Deere vs other high torque engines. Thanks for the advice.
 

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The problem is really going to be propeller size. I had a 22x35 strapped to a Sisu and it was no problem at all for it to spin, in fact it needed more pitch, a lot more. I don't know if you're running a cage or that's just the propeller you have but it seems small for a 36.

A bigger engine is going to be more weight, and if there's an issue of lifting the bow now, more weight isn't the answer at all. I have looked and I can't seem to find any torque numbers for the Deere's, something I find strange, absurdly so. A slow-turning engine is probably going to be your best bet and wind the pitch to it. I wouldn't consider anything over 2300 rpms, but that's just me.
 
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thanks first team

This is a big help, perhaps a different prop will help. No cage on the boat. The max torque is 578 lbs-ft @ 1800 rpm. 2600 rpm is the max for that engine. I get the weight in the bow we will keep that in mind. Thanks. I know this will not get me to 20 but if we pick up 1 to 2 that maybe all we can get with this engine. Thanks again.
 

captainlarry84

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A lot of good advice on this post.

Lightening bow weigh will help performance.

Removal of the keel cooler will give you at least 1 to 1.5 knots. The amount of drag from the keel cooler is amazing.

Your bottom should also be looked at. The removal of all old bottom paint and rough surfaces always helps.

A wet tube also helps but it is a big install and it may not be worth it.

Once all improvements have been made the last thing is to target your propeller.

With the above done, your boat should be photo tached at WOT against your current wheel. Depending on the RPMs the wheel should be adjusted. If the RPMs are correct I would still send it out for a complete re-con to see if you can pick up a few RPMs.

Lastly so I better understand give me the following:
HP at what RPMs
Speed at WOT & current RPMs
Speed at max cursing & at what RPMs
Reduction gear
 

Parttime

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Here's the specs on a 6068 200hp deere.

Hope it helps.

Intermittent Rated Speed 200 hp (149 kW) @ 2400 rpm
Peak Power200 hp (149 kW) @ 2400 rpm
Peak Torque579 lb-ft (785 N.m) @ 1500 rpm
Bore x Stroke–in. (mm)4.17 x 5.00 (106 x 127)
 
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thanks for all of the help

The bottom has been soda blasted and fared. Not sure what is going on the bottom yet. It is a twin disk 506. Thanks for the specs on the engine. I appreciate all of the help.
 

Poco Loco

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How does a shaft tube increase speed?
Is it the weight savings from the volume of water
in the keel?
 

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Not only that but you don't have all of the dead wood from the stern post, much nicer entry for the water flow to the propeller. You get to drop the weight of the bronze stuffing boxes as well. Good stuff all the way around.
 

eyschulman

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6068

Parttime is your 6068 one of the JDs that can change ratting with a chip? So if is 200hp at 2400rpm intermitant is there a M4 ratting at 2600rpm. I know the newer JD 6068s are that way I just bought a couple at 330hp at 2600rpm but the same motor with diffferent chips ranges from low 231hp M1 up to 330hp M4
 

Parttime

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Parttime is your 6068 one of the JDs that can change ratting with a chip? So if is 200hp at 2400rpm intermitant is there a M4 ratting at 2600rpm. I know the newer JD 6068s are that way I just bought a couple at 330hp at 2600rpm but the same motor with diffferent chips ranges from low 231hp M1 up to 330hp M4

I don't own a 6068. I found the info on the internet.
The motor in my boat is a cat. 3208 375 hp. Sorry for any misunderstanding.
 

captainlarry84

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A shaft turning is a keel full of water is friction drag on the shaft. With a wet tube a small stream of water is pushed down the shaft. With the water being push down the shaft there is no friction drag on the turning shaft which makes a difference.
 

lobster783

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shaft tube?

Aren't that wet keels designed to keep water/weight low in the boat and reduce roll? Does the shaft tube affect the performance of the boat in a heavy sea?
 

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Wet keels were designed to feed water to the shaft with the bronze running gear that wooden boats had. Wooden boats don't have hollow keels, but they have holes for the water to get to the shaft. Wooden boats were used as the plugs for fiberglass molds. No one is going to fill all that keel space in on a fiberglass boat so it was hollow, therefore when holes were poked for water to get to the bearings the entire space filled up.


Less weight, less drag, gets you back into port quicker during rough seas.
 
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