repower 1986 convertable

[pjreed]

I would like to hear from anyone who has repowered a 1986 36 with diesels and what there cruising speed was and what you repowered with.
Thanks Peter Reed
Pjreed@comcast.net

[Hatt36]

I have an 84 36 that was repowered with 330B cummins. With a full load, I cruise about 20 knots. I have added a 50 amp isolation transformer, air conditioning and a hard top with full curtains, so my boat weight is probably above average. The calulators on the boatdiesel web site suggest that over 500 hp per side would be required to get a cruise in the 25 knot range. If I were repowering now, the Cummins QSB or QSC series probably would be my choice.

Richard

[ADaily3224]

I have a 1988 36 Sedan, repowered with 350 HP Cat 3116 turbo diesels. On my last run of the season with water and head pumped out and about 100 gallons of fuel my performance was as follows.
1,200 RPM = 9.6 MPH
1,600 RPM = 12.0 MPH
2,000 RPM = 16.0 MPH
2,200 RPM = 18.0 MPH
2,400 RPM = 21.0 MPH
2,600 RPM = 23.0 MPH
2,900 RPM = 26.0 MPH Normally WOT is 2,850 but I was a bit light.

24x26 props, 1 3/4 shaft, 1.92.1 gear ratio. Most of the time I run at either 1,200 RPM or 2,200, very rarely will I run it over 2,200 as it's smooth quiet and economical at 18 MPH.

The 1983 to 1988 36's need a pretty good push of power if you want to go fast. When I'm full of fuel, water, people I loose some speed at the same RPM, as much as 2 MPH. I would suggest you don't go below 400 HP a side if you want modern boat speeds. On the plus side, for a 36 foot boat the handling is outstanding. The 2nd generation 36's were one of the few boats Hatteras built that were Jim Wynn designs, they are a deeper V and require more power than the older 36's.
Good luck with your project, they are a nice boat with the right power.
Tony D

[Maynard Rupp]

All very interesting as we are always considering changing our 1986 36C to diesels. We just ran the boat for a solid month, actually 28 days to Florida. As I watch gas prices fall below diesel and read the performance stats listed here, I am not about to switch. Our 36 with Crusader 350 hp. engines cruises at 18 knots @3200 rpm and does 23 knots full throttle. Where diesels do a better job is at displacement speeds as the best we can do is 1 nautical mile /gallon. We have a Navman fuel flow system and it is now perfectly callibrated, owing to the 231 hours we ran it last month. For that entire time we averaged 11mph and also averaged 13.1 gph. When I change oil, I need 2 cheap filters and 14qts. of oil for both engines. Overhaul costs are about 10% of the cost of diesels. I think one reason that these boats perform OK with gas engines is that Hatteras advertises the weight as the same regardless of powerplants. I do know that our engine packages with transmissions weigh less than 1100 lbs. each. I am also told that the tranny on a diesel weighs that much and the engines weigh about 3 times as much as the gas engines. That advertised weight of 26,500 lbs. can't possibly be true for both engine combinations. I am sure our gas engines will run well beyond 2000 hours with good care. I am not sure a turbo diesel will bo much better.

[SKYCHENEY]

Maynard,
I agree that overall cost of operation probably doesn't justify a repower to diesel for the 36 especially if you don't put many hours on her per year. I disagree, however, that a turbo diesel won't go more than 2000hrs between overhauls. The right diesel setup, propped correctly, and well maintained should at least double the life between overhauls. I've got 3500hrs on my 6v92TA's and they are still going strong. I would think modern diesels that are not pushed too hard should do even better. The biggest gas vs diesel issue today for boats like yours, though, is the ethanol problem. I think you stated that yours was made with the "good" resin, so you are one of the lucky ones.

[67hat34c]

if i was to repower yours i would go with cursader big blocks with mpi. I think you would see a significant improvement in the low speed economy. you could most likely keep same tranny and shafts prop change most likely. Diesel would be a waste of money.

[Boatsb]

Dan that boat of yours is about the biggest and heaviest I would consider for gas power. Diesels do have the durability in their favor but the next consideration I see is the amount of torque you get from them at cruising speed. They just seem to be stronger longer. As boats get larger though the gas option fades as more torque ( not HP ) is needed to plane them and the gas engines are not powerfull enough to move boats over 30K lbs efficiently. Cost wise the crusager big blocks ( 4 bolt ) you recomend are probably the best gas option. I also looked at the 6.l small block at 350+ HP as a smaller engine but only available in standard rotation.

[Maynard Rupp]

The big block 4 bolt main Crusaders are the only gas engines I would consider. The late model 36 Convertable or the Sedan Bridge models are about as big as you can go with the gas engines. Performance is very good, but if you really need to go real fast, buy an airplane. Actually at 23 knots the 36 is a little squirly and very sensative to trim tab position regarding roll, or lateral stability. I just can't imagine that hull throwing enough water aside to achieve speeds in excess of 30 knots. That would take more horsepower than you can cram in there and more fuel burn than I can afford. Someone here said that the performance of theirs is very dependant on weight. I agree, but the size and weight of the engines necessary for high speeds would probably be counter productive. Our boat really is a very nice performer with the Crusaders and the performance stuff I have seen for dirsel powered versions are very similar. The other good news is that if you ever wanted to change to diesels, this boat is already set up for them completly.

Yes, Sky, the very big concern is Ethanol. On the way to FL, I bought that stuff in NY and NJ. They have a big tag on the nozzle that tells you it contains 10% Ethanol. The stuff even smells like alcahol. I don't think any other states use it at this time. I just read an article that UL removed their approval for E85 pumps. Corrosion of the metal parts is the problem. Of course, how stupid can we be. That stuff collects water like crazy and water will surely corode the internal steel parts of any pump. That is the stupidest idea this country has promoted.

[SKYCHENEY]

Maynard,
You probably were already running ethanol when you were in Michigan. After Jenny pushed through her alternative fuels bill, we no longer had to label pumps that contained up to 10% ethanol. So, most of the gas in MI now contains it. You just don't know it. We also get a 5.1 cent credit at the wholesale level for this stuff, so you can bet that almost everyone is using it.

[ADaily3224]

Getting back to the original issue, the owner of the 36 1986 Hatteras does have a fuel tank issue. Is it worth tearing up the deck, replacing the tank, and when you're all finished you still have a gas powered boat? I think that's the real question, performance not withstanding.
So, "what would you do"?
One option could be to sell the boat you now own to buy a replacement with diesels. You'll take a hit on yours because of the controversy surrounding the fiberglass tanks and the new ethanol blend. Add to that the commission and cost of selling, and the commission and cost of buying. It starts to ad up. Twenty percent in commissions, maybe transportation costs, surveys, and the inevitable repairs you will encounter, pile all that on the low price you just got for a gas powered boat it might just start to make sense to repower. At least when your done you know what you have, brand new power and all the confidence that goes with it.
Me, I would drop in the diesels, pick up some speed, performance, reliability, fuel mileage, and resale. You really have to like you boat to do it, it's a big commitment.

Tony D