Repowering a 58 for trawler speed

[MikeP]

I like to tell this story...

When we bought our (non-stabilized) 53MY and took it to NY from about 30NM north of Philly, we encountered really nasty conditions in the Delaware bay, heading for Cape May. We held 10+ knots through the bay and then entered the canal. We stayed the night at a marina in Cape May.

We were at the bar that eve and ended up talking to a bunch of sport fisherman who had been out in the bay that afternoon. One of them pointed to his boat, a Viking SF in the high 50 ft range and said, "That's a 35 Knot boat! We couldn't do better than 9 knots out there today, I can't imagine how slow you must have had to go in that Motor Yacht!" I didn't have the heart to tell him that we were going faster than he was! Nothing was displaced or tossed around. The boats are definitely capable of handling whatever!

[yachtsmanbill]

Thanks Bill,

Whats the hull speed of a 58?

Someone here posted the constant for figuring hull speed, and if I remember correctly, the 58 with the cockpit extension (65 LOA) was around 10.4 mph.
The gps shows a good day on the TennTom around mile 401.
1400 rpm seemed to be around the "sweet spot". ws

[krush]

a little insight on hull speed: http://www.boatdesign.net/forums/showthread.php?t=1220

Bill, I think I'm just gong to install a boiler and steam engine. We'll just stop every so often to gather wood LOL

[Pascal]

"Something else just occurred to me...How are 58's in sloppy conditions at 9 knots? These appear to be a bit top heavy (Could be wrong) and perhaps were never intended for life in the slow lane. A MY is not the same as an LRC afterall.

Any 55-60 owners care to comment? Ang??? Freebird???"

head on, they're fine... waves dont' stand a chance against the mass of a 1510. when the seas start coming on the beam, they roll.... probably a little more than other boats with a lower CG like the LRCs. Depending on how you use the boat, it cna be a small trade off for the extra livign space....

hull speed is 1.33 x sq rt LWL on the 53, it's about 9.2kts. when you get close to 9 kts, you're fuel burn goes up... you really feel it just looking at the wake.

the 1510s are more economical at that speed than the wider beam, newer models like 54 and 56.

[Passages]

OK, so looks like hull speed assuming actual LWL of 52 feet is about 9.5 knots.

Now to Krush for the bonus question. Assuming vessel weight of 61k lbs, WL of 52', how much total hp is needed to provide continuous duty of 9.5 knots.



BTW, there is a calculator over on Boatdiesel.com but you need to be a member to play with it. Any members out there?

[Avenger]

You could get a detroit series 40 (it's a 4cyl 60 used in metro busses).

The 40 series 7.6 and 8.7L is a re-branded Navistar DT466E and DT530E. They may have a 4 cyl version of the 60 in the lineup, but I think you're thinking of the 50 series. All really good engines, BTW.

Drystack, huh? Now think about the look of a 58 with no flybridge and a funnel.... Hmmm, sounds pretty "yacht"-like.

[Brian Degulis]

Those Cummins would be a great choice, but they would cost more than the boat that he wants to put them in! A pair of 6-71's worked just fine for the LRC's and they'll work fine in that boat as well. I bet he can find a fresh pair of 6-71's and get them in the boat and still have only spent $100k for the whole thing!

The Cummins QSB 230s cost me around $15,000 each new. A rebuilt 671 outrite cost me around $13000 and your comparing rebuilt to new. Get past all the BS and look at as a project your going to do and the answer is obvious. You don't tear a boat apart to re power and put T Rex in a smaller version back in. The DDs were great but the operative word is were they are absolute junk compared to what's available today. With new electronic engines you will have a 2 year warranty it will be much quieter and smoother it will burn a lot less fuel parts are current and it can run at any RPM continousily without fear cold burn. As a bonus just think of how happy Al Gore will be!!!!!

Brian

[Genesis]

If you can get QSBs for $15k new you'd be nuts to put 6-71s in there for $12k each.

Absolutely insane.

There is no comparison between those engines, and folks, I'm a BIG fan of Detroits.

The facts, however, are what they are. The social and fuel aspects of the QSBs are immensely favorable.

If I had the 6-71s and needed to buy kits and heads I might be inclined to rebuild them (myself) but starting with empty engine rooms?

That one's easy.

[ThirdHatt]

My mistake, I thought the new Cummins QSB's were more like $25k each so just the engines were going to be $50k. That's probably what the boat will cost to buy. At that point, like Passages (the guy actually considering this project) said if it is Detroits for half the price of the Cummins, it's Detroits all the way. If the cost of Detroits is actually anywhere in the ballpark of the new Cummins I agree, no brainer. Cummins all the way. Not sure if the 230hp vs the 280-300hp makes much difference in this application.

[krush]

The 40 series 7.6 and 8.7L is a re-branded Navistar DT466E and DT530E. They may have a 4 cyl version of the 60 in the lineup, but I think you're thinking of the 50 series. All really good engines, BTW.

Drystack, huh? Now think about the look of a 58 with no flybridge and a funnel.... Hmmm, sounds pretty "yacht"-like.

I was thinking the 50 series. I don't know why the heck I said 40--didn't even know a 40 series existed.

If you don't plan on ever really going faster than 10 knots, then getting a smaller engine and running it closer to max output should give you the best fuel burn....but that isn't a huge concern if you plan on only doing 100 hours a year. The engines will rust away before you wear them out.

Re: look of a drystack. Functionality trumps all looks in my book