Buy Duffy 35 and repower - your thoughts?

andy65

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Looking at a 1985 Duffy 35 with a 300 hp Caterpillar 3116 with 600 hrs installed in 1996. Advertised cruise is 13kts. I will use it for cruising. I'm not going to be happy at 13kts. Would like 18. And I'm concerned that a 17 year old engine with little use may be on its way out due to age not hours. The 3116 is not known as one of Cat's better engines. So, I'm thinking buy and repower with a Cummins reman.
- What are the cost factors to consider? What would you budget? I don't know the shaft size. What HP?
- Technical gotcha's such as angle, relocate engine due to weight, won't fit, extensive structural work and tearing out the floor.
- What do you think the used Cat would sell for to offset some of the cost?
- I'd want to take the flybridge off. It is nice. Is it worth much?
- How much will cruise speed benefit from removing the flybridge and canvas.
- Is 13kts realistic with 300 hp in a Duffy 35?
Trying figure what price I'd have to get the boat for to make it viable. There are some Duffy 35's out there for under $100k but they all seem underpowered.

It is the Duffy in Greenport if anyone knows the boat.
 

Powderpro

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What size of prop is on the boat currently and what size will fit under the boat? If it has a 26" currently or a 26" will fit, then that will definitely help your speed potential if you install more horsepower. What shaft size does the boat have? Hopefully it has at least a 1.75" diameter aquamet 22 high strength. But 2" is preferable and better.

What Cummins Recon are you thinking? I would think if you want a solid and consistent 18knot cruise, you would want to go with the C-series 8.3 430hp Recon. Another option (a better option in my opinion) is a new 6.7 liter Iveco 420hp or 450hp. It's going to be about the same price as the 8.3 Recon, but the Iveco weighs about 500 lbs less, and has a smaller footprint and probably weighs about what the 3116 Cat weighs. Plus the Iveco would be a much quieter engine. The 8.3 Recon and the new Iveco 6.7 will both cost in the ballpark of $27,000 - $30,000 bobtail.

Removing the bridge may gain you a knot in top speed?
 

captainlarry84

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Your 35 Duffy is most likely wet keeled as apposed to wet tube. The boat will take a 26 wheel so you can get plenty of HP into the boat. Most likely the current shafting is 1 with a 506 TD gear and your 3116. I would EST the value of your old power & gear as a running takeout @ 5K.

If the boat has 1 shafting you will need to up grade in to 2. Because it is a wet keel it will just require a new bronze stern tube housing & stuffing box.

On a recent repower the Cummins 8.3 @ 550 HP fit into a Duffy under the floor, however that Duffy had a wet tube which may allow the motor to sit deeper. This boat is still being wheeled with a 26 propeller the boat cruises at over 20 knots with a full F/B>

On a second Duffy repower with a wet keel the owner wanted to stay with CAT power. A 3208 375 HP was removed and a C-7 CAT was installed. The C-7 gave the boat a 17 knot Cruising speed. The boat has a 2:0 gear & a 26X 22.5 ZF Propeller. The owner wanted the C-9 however it would not fit. The C-7 is the same foot print as a 3116 however it requires a larger gear either a 507TD or a ZF 285a. Therefore you save no work by staying with a CAT.

The two motors I like for the 35 Duffy are the Cummins 8.3 either 500 of 550 HP or the Yanmar 480 with a 2.5 gear may also give excellent performance.

This is a big ticket repower. New motor, re shafting, twin controls, new propeller odds 7 ends I would round # EST the total job @ 60-65 K.
 

islander

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Andy there are lots of variable to consider. These projects often come with more complexity and more time and cost than we originally thought. Perhaps if you can buy the boat at the right price than go for it. It would be wise to also hire a diesel engine mechanic to go thru that engine before purchasing. They should be able to give you information that about that engine, that would help you in that decision before you take the plunge.

There is also forum dedicated to boat diesel engines. http://boatdiesel.com There is a guy on that forum located here on the west coast (I am sure the east coast has a go to guy as well); who is a cummins expert and is east to talk to. I can pass his name along of interested. Located next to that guy is my Cat mechanic; I have a CAT3208 who is REALLY knowledgeable on CATS and may be able to shed light on the engine in your prospective CAT.

Knowledge is power!

Good luck!
 

andy65

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Your 35 Duffy is most likely wet keeled as apposed to wet tube. The boat will take a 26 wheel so you can get plenty of HP into the boat. Most likely the current shafting is 1 with a 506 TD gear and your 3116. I would EST the value of your old power & gear as a running takeout @ 5K.

If the boat has 1 shafting you will need to up grade in to 2. Because it is a wet keel it will just require a new bronze stern tube housing & stuffing box.

The two motors I like for the 35 Duffy are the Cummins 8.3 either 500 of 550 HP or the Yanmar 480 with a 2.5 gear may also give excellent performance.

This is a big ticket repower. New motor, re shafting, twin controls, new propeller odds 7 ends I would round # EST the total job @ 60-65 K.

Appreciate your insight. 60K Yikes!
How would you approach the project to make the most use of what is there i.e. What is largest reasonable HP for a 1 3/4 shaft? What kind performance might be expected? I was thinking in the 425 HP range. Still need a different transmission? I would remove the flybridge.


there are lots of variable to consider. These projects often come with more complexity and more time and cost than we originally thought. Perhaps if you can buy the boat at the right price than go for it.
Right on. My concerns exactly. I have seen so many boats with diesels replaced after 10-12 years that I think it is wise to allow for the cost of a repower within the next couple of years.

Any known problem areas on Duffy's of this vintage for when I look at the boat? Are they cored below the waterline?
 

islander

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Andy my boat is solid glass below the water line. If you can get the HIN from the seller you may try calling Atlantic Boat company and perhaps they can tell you the specifics for that boat.
 

captainlarry84

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I found your boat on yacht world. Another rub in a repower of this vessel is that you will have to cut the hardback out, which was not figured in my very low round # quote to do the repower.
It is a beautiful looking Duffy & price fair. Based on the ask most boats like this will sell for 65 to 75% of the asking price.
300 3116 with a full F/B the boat will most likely cruise at 12 knots @ 2400 RPMs and 2400 RPMs is the max cruise RPMs. Should you seatest the boat make sure it gets the full 2800 RPMs..
Prior to the 3208 375 HPCAT in a Duffy with no F/B the boat only cruised at 13 knots at 2400 RPMs.
It is a good buy if you are happy with the vessel as is. A repower…..$$$$$
 

andy65

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Am on the ferry to look at it. What is the hardback? I see a lot of cabinetry that may be in the way. Only 13kts with 375 hp? Or did I missunderstand. May have a live report late afternoon.
 

captainlarry84

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Hardback is the term used for the rear of the wheel house. The door opening is not large enough to slip in a repower. You read correct a 1991 Duffy no F/B 375 CAT Solid glass hull 300 gallons of fuel only 13 knots @ 2400 RPMs
 

MASTERENEGADE

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Larry: Im not questioning your knowledge, but 13knts seems very slow.

The westlake out of montauk eddie millers old boat before he past away was a 35 duffy with a 3208ta(375hp) f/b, generator, and i believe 300gals of fuel. It used to cruise at 16-17knts. I ran that boat with him a number of times to the canyons, capecod mackeral runs and such. That boat moved right along.

So something there doesnt seem to add up.
 

petrel

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That doesn't sound right f/ 375 hp. I thought 35 Duffys went pretty well. I can do better than that in my 1980 wet keel 31' BHM w/ 315 hp and a 2.5 to 1, 26 square four blade. 16 knots at comparable RPMs. And she has no problem turning the wheel.
 

captainlarry84

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I am sure that his old low sheer 35 Duffy may have done 16-71 knots. But not the one I am talking about. 13 knots was the speed. With the 3208 @ 2400 RPMs and she only could swing a 24 X 23 wheel. A very heavy boat. Also keep in mind that old CAT power did not put out much HP @ 2400 RPMS on about 240 of the 375 was in use.
My 31 JC with the 3208 320 CAT towards the end was only 14.5 knots @ 2400 RPMs.
3208s were great motors, however they did not have a good user HP range at cruising speed.
Your 31 BHM with a 2:5 gear & 315 HP should give you 16 knots no problem with a 26 square.
Even after the repower with 460 HP the cruise speed was only 17 knots. These are true numbers.
 

MASTERENEGADE

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Larry: You are right on the low sheer. The westlake was i believe an 1986-87 low sheer duffy. I didnt realize there was that much of a weight difference between a low sheer and high sheer 35'duffy. Im always learning.
 

starrfish

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just for some more comparisons, i had a 375 HP 3208 before i repowered my 35' duffy, and at 2400 she cruised at 16/17 kts, with 300 gal of fuel, solid glass boat, no fly bridge, she weighed 18500 lbs, with 150 gallons of fuel in it.
since i repowered with a 3126 420 hp cat she cruises at 19/19.5 kts, 24x24 medium cup prop, and the twin disc gear was the same on both (old and new) motors #507 2:1, she burns 14 gph @2400
 

BillD

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Hardback is the term used for the rear of the wheel house. The door opening is not large enough to slip in a repower. You read correct a 1991 Duffy no F/B 375 CAT Solid glass hull 300 gallons of fuel only 13 knots @ 2400 RPMs

One more additional term I hear is "winter back" .
 

petrel

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I guess most of the Duffys I've seen must be low sheers....

I think a "winter back" comes off f/ the summer.
 

captainlarry84

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Starfish your repower sounds like a home run. I am sure she runs real sweet. You have a leg up with 150 gallons of fuel. 300 gallons in the back make a very big difference in performance. Duffy’s run well and it is by far one of my all time favorites. Although Mr. Flower’s unique design of a built down bow with a skeg designed stern section and magnificent keel design keeps wink at me as the perfect DE boat. His hulls can take the big power with great wheel aperture and hull sex appeal.
The 35 duffy that was repowered with the Cummins QSC8.3 liter 550HP @ 3000rpm is a home run. She is quiet smooth and very fast. The attached photo shows the install. A very fine pro install.

IMG00062-20120218-1135.jpg

March photo 06 437.jpg
 

andy65

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Reporting in: saw the boat today. It really is in nice condition. Motor mounts are quite rusty and some on the transmission but that is to be expected. Owner says cruise 14kts top 18. Probably right. Maybe 12 to 14 my guess. A little light for me. Boat is clean an cared for. Engine hatch is 31". Hardback door is wider. 1 3/4 shaft 24" prop 31" hull to skeg. I could id the transmission but have s/n. bottom line a nice boat. But with a 19 yr old engine it has to be due for some work even with the low hours. Right?
 

captainlarry84

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Andy, I concur with Islander. CAT power is good power. The boat you are looking at is a yacht finished Duffy. If you love the look, which I do..deal with the power & speed and move forward the 3116 is a 1999 and they were good motors the only draw back will be the lack of speed. An excellent gauge to add to your CAT panel is a pyrometer. The meter measures exhaust temps and it can prolong the life of any diesel engine. On today’s electronic motors they call it a load meter. You need to know the temp specs of your CAT then run the motor at 75-85% of max load. Example: The max pryo temp on my Yanmar at WOT is 1280 degrees. Therefore the max I run my boat at 1080 degrees which is 85% load. Most of the times I run at less.
The pryomter is the guage all the way to the left.

Picture 028.jpg
 
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