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-   -   Repower confusion (horsepower) (http://www.sailnet.com/forums/diesel/96305-repower-confusion-horsepower.html)

jrd22 02-02-2013 09:29 PM

Repower confusion (horsepower)
 
Went to the Seattle boat show yesterday to look at a couple of different engine options for a repower and just to see what was new (haven't been for several years). I answered some questions I had(Beta is at the top of my list now), but came away with some new ones regarding how much horsepower I need (or maybe how much I can use is a better way of putting it). The rep for Beta had a nifty program on his computer for determining hp requirements and for our boat he recommended the 38 hp model. The original Volvo we have now is 62 hp. His recommendation is based on the following specs for our boat, prop, etc.
LOA 40'
LWL 35'
Disp 23,000 lbs (26,000 loaded for cruising)
Beam 12'8"
Prop 18" X 12 fixed three blade sail (will probably install 3 blade Max prop)

His program showed that with only an 18' prop there is no way we can use all of the horsepower we have and a 38 hp engine would drive the boat at hull speed at WOT. I would at least go to the 43 hp model because it is a lower rpm engine and jumps up to the heavier duty trans., but even that is a huge drop in hp from what we have now. I like to run things easy, we motor at around 26-700 rpm now (3500 rpm WOT) which gives us a little over 6 knots. The sail prop doesn't give us a lot of thrust, I think we would gain quite a bit of speed with the max prop. The smaller engine would be easier to install, and cheaper, but even 43 hp seems low to me.

So I'm curious, those of you with similar size and displacement boats, what horsepower and prop size do you have, and what speed/rpm do you get out of it? Thanks!

PorFin 02-03-2013 03:29 PM

Re: Repower confusion (horsepower)
 
jrd,

Our boat's got very similar specs as far as LOA/LWL/DISP go, and has a Perky 4.108M installed.

Although the 4.108's rated at 50 hp, that's at max rated RPM (4k) WOT when the stars and planets are precisely aligned; in practical terms we typically run it in the 2200-2400 rpm range for cruising, and with a spanking freshly cleaned hull in dead flat conditions we can go at hull speed (three bladed 16-10 prop). While my memory is fuzzy, I think at those rev's we're looking at around 30 hp output.

SloopJonB 02-03-2013 04:02 PM

Re: Repower confusion (horsepower)
 
JR, the old rule of thumb of 4 horses per ton would put you at 52 HP in cruising trim.

Of more importance than the horses is the torque and its curve. Are those horses Clydesdales or Quarter horses. :D

If the torque curve of the Beta gives you adequate grunt at 2800, you really don't need more. The 4 per ton "rule" goes back to the days when sailboats pushed a lot more water out of the way than they do now. My friends Hunter 38 is probably about 20K Lbs in cruising trim with a Yannie in the 30's - it has lots of power at 2800 in that application - we've never needed to run it to 3000 even when bucking our local currents.

Minnewaska 02-03-2013 04:11 PM

Re: Repower confusion (horsepower)
 
You want to have enough power to push the boat to hull speed with oncoming waves at only 75-80 of max rpm. Who would want to run their motor at WOT? Then you want to be able to run an accessory or two, should you choose down the road: spare alternator, engine driven emergency pump, fridge compressor, watermaker pump, etc.

If you have a few extra HPs, you can pull the throttle back and deal with it. If you have too few, you have no options.

jrd22 02-03-2013 04:56 PM

Re: Repower confusion (horsepower)
 
Thanks for the replies, I just assumed that I would replace it with an engine of comparable hp. The program that the Beta guy used went into blade loading, efficiency, etc and it seemed pretty conclusive that even with increased pitch an 18" wheel just couldn't use all that horsepower. Everything else in the drivetrain is overkill too (1.5" shaft, Walter V-drive good for 150 hp, etc.) so I should have figured the engine had more hp than required. If I pull the trigger I think I'll go for the 50 hp model, I'll still be saving a bit of weight and $$, and it should fit back in the "hole" a bit easier too.

chef2sail 02-04-2013 12:38 AM

Re: Repower confusion (horsepower)
 
JR,
Interested in why you are choosing the Beta. Could you rank your choices and give me some f your pro and cons of each in your research.

Dave

jrd22 02-04-2013 02:05 AM

Re: Repower confusion (horsepower)
 
Chef- I had it down to a short list of the Beta 60 and the Cummins 3.3 from Transatlantic Diesel (65hp). I also looked into the Yanmar and Volvo but rejected both because they use a turbo and I wanted naturally aspirated (I have nothing against turbos on larger diesels but feel they are an unnecessary complication for small sailboats). I did not look at Westerbeke mainly because of the comments about high parts prices I have read here (I have Volvos, been there, done that), but I'm sure they are good engines and maybe I didn't give them a fair shot. The Cummins is a great engine but Transatlantic is the only place that marinizes them and there aren't too many around. I also talked to a Cummins rep and he questioned whether Cummins would honor the warranty(I think they would) in a marine application (they're an industrial engine) which gave me some doubts. I rejected it because I want to go with something more mainstream.
In my former business I had several pieces of equipment that used Kubota engines and they were reliable and almost impossible to destroy, even though we ran them in the absolute worst conditions imaginable. Beta has a good reputation and people with them seem universally happy with them based on the threads here on SN. I like the fact that they aren't trying to squeeze every last HP out of the engine by using a turbo and intercooler, and that it's a slow rpm engine with a fairly flat torque curve so it should be able to maintain speed into rough weather. I also want to reduce the noise of the engine in the pilothouse and the lower rpm should help a lot with that (the Cummins puts out almost 55 hp at 1800 rpm, which was a big plus in my book). After actually seeing a couple of the Betas at the show I was pretty impressed with how they've done things, it looks simple and I didn't see anything that I didn't like. Beta also offers custom mounts which will make the installation a lot easier (current engine has much wider mounts than most and at two different elevations). I also liked that even though I was set on the 60 HP model the Beta rep spent quite a bit of time convincing me that I didn't need it and could save money by dropping down to the 38 or 43 hp model (big savings for me, much smaller sale for them).
Bottom line, I think almost all of the various engines offered are probably good, you just need to find one that you're comfortable with and doesn't pose too many difficulties changing over from what you currently have.

chef2sail 02-04-2013 02:49 AM

Re: Repower confusion (horsepower)
 
Quote:

Originally Posted by jrd22 (Post 985328)
Chef- I had it down to a short list of the Beta 60 and the Cummins 3.3 from Transatlantic Diesel (65hp). I also looked into the Yanmar and Volvo but rejected both because they use a turbo and I wanted naturally aspirated (I have nothing against turbos on larger diesels but feel they are an unnecessary complication for small sailboats). I did not look at Westerbeke mainly because of the comments about high parts prices I have read here (I have Volvos, been there, done that), but I'm sure they are good engines and maybe I didn't give them a fair shot. The Cummins is a great engine but Transatlantic is the only place that marinizes them and there aren't too many around. I also talked to a Cummins rep and he questioned whether Cummins would honor the warranty(I think they would) in a marine application (they're an industrial engine) which gave me some doubts. I rejected it because I want to go with something more mainstream.
In my former business I had several pieces of equipment that used Kubota engines and they were reliable and almost impossible to destroy, even though we ran them in the absolute worst conditions imaginable. Beta has a good reputation and people with them seem universally happy with them based on the threads here on SN. I like the fact that they aren't trying to squeeze every last HP out of the engine by using a turbo and intercooler, and that it's a slow rpm engine with a fairly flat torque curve so it should be able to maintain speed into rough weather. I also want to reduce the noise of the engine in the pilothouse and the lower rpm should help a lot with that (the Cummins puts out almost 55 hp at 1800 rpm, which was a big plus in my book). After actually seeing a couple of the Betas at the show I was pretty impressed with how they've done things, it looks simple and I didn't see anything that I didn't like. Beta also offers custom mounts which will make the installation a lot easier (current engine has much wider mounts than most and at two different elevations). I also liked that even though I was set on the 60 HP model the Beta rep spent quite a bit of time convincing me that I didn't need it and could save money by dropping down to the 38 or 43 hp model (big savings for me, much smaller sale for them).
Bottom line, I think almost all of the various engines offered are probably good, you just need to find one that you're comfortable with and doesn't pose too many difficulties changing over from what you currently have.

Thanks for the reply. I think that Beta is a good engine. I have a friend whoi is a SN who just installed one. I agree with you phiosophy about the turbo. I feel the same way about an extra thing to complicate it. And volvos are just to expensive to repair.

I guess the reason I asked though is that I prefer the Yanmars slightly. For many of the same reasons you enumerated plus the Yanmar was not a converted engine and was built originally as a marine engine

I thought the 53 Hp Yanmar 4JH54 was a normally aspirated one and that it was the 73 HP 4JHTE was turbo charged.

Minnewaska 02-04-2013 07:22 AM

Re: Repower confusion (horsepower)
 
I agree, turbo chargers on sailboat diesels are evil. Some argue they are more fuel efficient at comparable HPs, but no doubt in my mind you will give it all back in turbo maintenance over time. I can only see them as useful, if you just don't have the room to hold the block of the size motor you need to push your boat as you like. This is a bigger problem with stinkpotters than sailboats.

I do not believe the entire line of Yanmars and Volvos are turbo charged.

One other thing to consider is the resale value of your boat. It seems the ubiquitous motor in the US these days is the Yanmar. I don't think its superior, but it seems to be the brand whose parts are most commonly stocked and the first certification the local yard wrenches get. If true, that makes it the easiest to deal with.

The idea that a diesel has been marinized from a common block is appealing, if you can buy non-marine parts or disposables. However, you have to be wary that you are not de-marinizing it in the process and are knowledgeable of the difference. How will the next owner feel about it.

Just some food for thought.

chucklesR 02-04-2013 07:39 AM

Re: Repower confusion (horsepower)
 
If you have the $$ go bigger, as said before you'll be wanting a little extra for altenator/watermaker/yada yada's that will be taking HP directly off the top (before it gets to the prop).

I'm surprised the software indicated only a 38 to swing the 18x2 x 3, but you don't mention the transmission and the reduction ratio so that's hard to figure.

It's a tad to early in the morning for me to reverse engineer the math on the amount of HP required to swing that diameter at 12 pitch to your hull speed.
I'm no naval architect, didn't stay at a hotel of any type last night etc.. but:

My dinky little Irwin 38 at 20k runs with a 44hp

Putting a smaller motor on bigger and heavier seems like underpowered to me.


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