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Old 03-12-2014, 12:10 PM   #21
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The OP has received some advice from current Sundowner owners that strongly indicates the install issues are paramount. Key to this decision is not only the engine selection, but the cost estimate from the guys doing the install and other peripheral work. Whether Beta, Yanmar or ??, over half the cost and maybe 90% of the problems will be due to the quality and skills of the outside labor if job is being contracted out.

Being located in MA, you should have several good yards to talk with about fit, ancillary work and schedule. Naturally, the group doing the install should be able to point (proudly) to their previous engine change out experience.
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Old 03-12-2014, 02:13 PM   #22
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Really cool calculator for determining hull speed and power requirements:

http://www.psychosnail.com/boatspeedcalculator.aspx

The calculator says I need 50hp to achieve hull speed (7.5 knts) in my Gulfstar 36. I have twin 52 hp Perkins 4-154s. If I were to replace them with something more efficient would I be looking at two 25-30 hp engines? Just trying to figure out how to apply this discussion to a twin engine situation.
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Old 03-12-2014, 10:42 PM   #23
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Hull speed need not be achieved at all. While cruising most all FD boats in our typical size will need 3 to 4hp per ton of displacement for max engine power. 4 to 5hp is more common though. My Willard has 5 and we have a 40hp engine. Only half of that is used to cruise a bit over one knot below hull speed. That gives me a 50% engine load and most engine experts recommend a bit more than that. I don't even know for sure if I can reach our HS of 7 knots. No need to know. I do need to know if my engine will achieve it's rated 3000rpm engine speed. But this all applies only to FD hulled boats. The Sundowner is'nt even close to a FD hull but we can guess that a typical SD trawler hulled boat will require about 1.5 to 1.75 times as much power as a FD boat to perform at about the same speed as the FD boat. That would indicate the Sundowner should need 60 to 75hp to cruise at the displacement speeds of same size FD boats.

However the Sundowner should be capable of going considerably faster with more power unlike our FD boats. The OP is in a position where he can chose to go faster or slower but his decision window will close the moment he buys his engine. Low or high rpm IMO makes no difference.

Some FD boats have only 2hp per ton but they are few and mostly larger craft.

On The Rocks,
Single or twin IMO makes no difference. What is your hp per ton? As a guess I'd be thinking two 40hp engines. I'm not that familiar w your hull either.
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Old 03-13-2014, 11:04 AM   #24
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Quote:
Originally Posted by On The Rocks View Post
Really cool calculator for determining hull speed and power requirements:

Boat Speed Calculator

The calculator says I need 50hp to achieve hull speed (7.5 knts) in my Gulfstar 36. I have twin 52 hp Perkins 4-154s. If I were to replace them with something more efficient would I be looking at two 25-30 hp engines? Just trying to figure out how to apply this discussion to a twin engine situation.
Most calculators are based upon smooth water. A few large waves will change things quickly as to required HP. Having 2X the calculated HP installed is not a problem IMHO, some of us have 4X and are quite happy about it.

Also to assume smaller engines running at 90% load would be more efficient is not correct, especially when assuming efficiency means total $ spent. Very good engine longevity at low RPMs and 20 to 40 % load is quite cost efficient in terms of maintaining and operating a lightly used boat. Rotating equipment wear goes up exponentially with RPM, about square or 4X for a 2x RPM increase.

Are your engines running OK? A good maintenance program will keep your Perkins 4s running for a very long time. Due to environmental regs they can't make them like your Perkins anymore, I wish they could.
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Old 03-13-2014, 01:42 PM   #25
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Tom,
Looking at the engine specs tells very quickly what engine speed is most efficient. However I think that's at WOT. I don't think there's much difference underway but running light is definitely not efficient hp per gal of fuel.

And as I've said before I've never ever increased power when in the nasty. And anything I've lost in speed is not noticeable.

And I'm sure no one runs at 90% load on this forum.

But I think your'e right about the OPs Perkins. Only reason I re powered is because we were going to the wilderness.
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Old 03-13-2014, 01:48 PM   #26
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And I'm sure no one runs at 90% load on this forum. .
On The Rocks indeed suggested that as a possibility or question.
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Old 03-13-2014, 01:55 PM   #27
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Not looking to replace the 4-154s fortunately they run great but parts are hard to find. I was really just trying to get my head around what the most efficient hp to cruise at or near hull speed with twins. I realize I'm never going to go fast in a FD hull so really just need enough to go 7.5 knts with enough reserve to handle heavy wind/current.
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Old 03-13-2014, 01:57 PM   #28
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Like many have said, much less cost and maint with a power package that does NOT have a turbo and intercooler. Also look carefully where you travel and your own skill at repair, if service and support is critical then need to look at the support network. In this area Yanmar has a very large support network, not sure of the Beta myself.
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Old 03-13-2014, 01:59 PM   #29
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Originally Posted by On The Rocks View Post
Not looking to replace the 4-154s fortunately they run great but parts are hard to find. .
What parts?
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Old 03-14-2014, 12:51 AM   #30
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Did we scare off the OP?

Paul, I have completed a similar re-power in my 26' Nordic Tug. I downloaded all of the information from all of the diesels that were in consideration (Beta, Hyundai, Isuzu, Iveco, John Deere, Mitsubishi, Nanni, Sole, Universal, Vetus, Volkswagen, Volvo-Penta, Westerbeke, and Yanmar) and made an Excel spreadsheet to compare...

I listed critical boat dimensions:
  • Top of engine bed stringers to underside of pilothouse hatch lid
  • width of pilothouse door w/ frame removed
  • width of pilothouse door
  • min height of pilothouse door
  • min width of passageway
  • min width of companionway doors
  • Distance between engine bed stringers
  • width of the stringers
  • distance from the top of the stringers to hull
  • propeller shaft flange to forward bulkhead

I compared ancillary equipage location:
  • alternator side
  • starter side
  • transmission control side
  • fuel inlet side
  • raw water pump maintenance clearance
  • fuel filter clearance
  • oil filter clearance

I compared engine dimensions:
  • front of engine to gearbox output flange (OA length)
  • Front of engine to forward mount
  • Front of engine to CL of rear mount
  • Engine mount to engine mount
  • Rear Engine Mount to Output flange
  • OA width
  • Mount to mount (CL) width
  • OA height
  • Crank to top
  • Crank to bottom
  • Crank to output flange

Now you know what will fit.

Of course price and delivery were compared along with critical spare costs.

I created hp and torque curves and plotted them on the same axis spacing (tricky engine manufactures change plot to make them look flatter) like the graph below.

Now you can play around with prop calculators, specific fuel burns and the like to optimize you cruising speed. Make sure you know your prop clearances.

Have fun!
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Old 03-14-2014, 07:08 AM   #31
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With a boat requiring such little HP to cruise I would play the numbers to cruise on the bottom of the engine builders reccomended RPM,

1200 if it was allowed or 1500 which is more common on tiny engines , that would be my LRC cruise goal.

The pleasure of quiet shake free long term highly efficient operation would be worth the numbers crunch.

Just try to find the Prime Genset operation specks for the engine . many run 1200 for decades.
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