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 Post subject: beta marine (again)
PostPosted: 22 Mar 2021 08:26 
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Skipper

Joined: 09 Aug 2017 15:35
Posts: 725
Location: Maine/USVI
I just got off the phone with Joe Demers at Sound Marine. We had a long discussion about repowering and he actually recommended against the Beta 38, Beta 35 AND the Beta 30, all in favor of the Beta 25. I explained the T37 factory dry weight does not reflect reality at 15,500#, and often shows well over 20,000# in the slings cruise ready. Not a problem.

What I'm hearing is any diesel should be run hard, and you'll never use the HP of the larger engines. The Beta 25 with gear weighs less than half the W50. Imagine the engine room space and the serpentine belt system.

I do know the 3YM30 I put in the Bristol 35 years ago was more than sufficient, and it would've been the biggest Yanmar I'd put in the T37.

Now, I know some of you put in the B38 and others the B35. Joe's rationale is that sailboat people wanted "get up and go" and many do a LOT of motoring. Norms have changed in that direction to an extent. But I don't motor unless it's the safest thing to do. And maybe dropping 250 pounds or so will stop that stern-heavy static squat. And the price is very, very appealing. At the same time I have to either rebuild a Detroit 4-53 screaming meemee or get a Cummins 6BT reman to pop into the Dyer 29. Everything is coming south. Charter businesses next season beginning December. Must fish, must sail.


 
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 Post subject: Re: beta marine (again)
PostPosted: 22 Mar 2021 09:37 
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Tactictian

Joined: 06 Aug 2020 09:02
Posts: 142
Diesels should always be run at or above 80% max load for service life and efficiency. Large marine diesels on ships are usually run up around 90% provided they are in good condition, and that is one reason why diesel electric propulsion is so attractive - multiple engines providing power allows you to reduce the number of engines on-line to get the desired load/speed combination.

None of this is rocket science. Any displacement sailboat has an effective horsepower curve which is basically just the power required to achieve speeds up to some notional "hull speed", which is a function of WL length, prismatic coefficient and other form factors. However, there are various power transmission losses that need to be accounted for (trans, gears, bearings, struts, etc). You also need to account for alternator power requirements (can be several hp when loaded). So, what you want to ultimately calculate is your required "SHP" which accounts for all of the losses to arrive upon a required installed brake horsepower for the engine.

If I still had access to design software (I used to use "NavCad" in my former nav arch life) and the T37 coefficients it would be relatively easy to calculate this BUT there is really plenty of anecdotal experience for this boat. We know that the W50 generates 41 hp at something like 3300 rpm. We also know that we want to have a proper prop, properly pitched, to reach something like 2600-2700 RPM for proper cruising speed (80% load by RPM). We know that under these conditions and with a clean hull/prop in calm water we can achieve something close to 6.7-7 knots boat speed (give or take). We also know that this speed is at the upper end of that EHP curve I talked about, so dumping more power into the water doesn't buy you much speed because the resistance climbs as the cube of the speed. At 2600 RPM the W50 puts out about 36 BHP but the actual delivered is probably several HP less.

What I'm getting at here is you can go with a less powerful engine BUT you had better be sure that you can get the desired boat speed when you add in other factors like alternator loads, less than perfect bottom/prop, wind/waves, increased boat loads. The W50, such as it is, can be loaded properly and can achieve desired speeds with some margin left for added loads. I suspect that you can go a few HP less that the W50 or W40 (properly geared and prop'd of course) but I would be VERY careful of going too low. You might just be fine in perfect conditions but you could easily run into powering a powering deficiency in averse conditions.


 
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 Post subject: Re: beta marine (again)
PostPosted: 22 Mar 2021 09:48 
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Tactictian

Joined: 06 Aug 2020 09:02
Posts: 142
I looked up the Beta 25: https://betamarineusa.com/portfolio/beta-25/

25hp at 3600 RPM. Personally, I think this far too little power for the Tartan 37 (as you noted, we're all displacing around 20,000 pounds). You would not be able to achieve much over 6 knots boat speed in anything but perfect conditions. Saving some weight is great, but being underpowered is no bueno if you want to put to sea.


 
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 Post subject: Re: beta marine (again)
PostPosted: 22 Mar 2021 10:46 
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Skipper

Joined: 09 Aug 2017 15:35
Posts: 725
Location: Maine/USVI
I'm hip to all that. I put a 2YM20 in a Pearson 10M, which weighed almost the same as my Bristol 35. 12,500# factory (vs. 15,500# for the T37) and we all know that can go up by 25% based on the T37 result. Admittedly, the Bristol had more wallop with the 3YM30, but I never had a situation with the Pearson 10M cruising the Caribbean (weekending, mostly) where I felt uncomfortable. I will also admit going to Jost 8 miles dead into 8 footers and 25kn wind was a pain in the 10M, but it was just a wet, slogging pain. And we won Ivan's Easteregatta that year.

You did make me think about a critter encrusted bottom.

It's down to the Beta 25 vs. 30, but the 30 jumps into the next larger engine category and weighs 57 pounds more. And it costs a little over $1000 more. But I think it would be all you'd need, especially with the serpentine belt, since no matter what, the W50 will always be stuck with a v-belt unless you invent, tool and build your own system.


 
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 Post subject: Re: beta marine (again)
PostPosted: 22 Mar 2021 12:11 
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Tactictian

Joined: 06 Aug 2020 09:02
Posts: 142
A few other comments. If the Beta 25/30 does have a serp, that just means you will draw more power off to the alternator. Also, you will likely require a new prop or a change in pitch on your current prop. You will definitely want to prop that engine such that you can achieve rated RPM for those times where you need every last pony. Personally, I don't want to be in that situation.

Another thing I forgot to mention and which your engine guy might now be taking into account - the shaft angle is another variable and will further increase required SHP and BHP.

Well, I hope it works out for you. At least you'll have a lighter boat and an engine that has better economy.


 
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 Post subject: Re: beta marine (again)
PostPosted: 22 Mar 2021 12:16 
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Tactictian

Joined: 06 Aug 2020 09:02
Posts: 142
Also, the P10M is a totally different story. Not only is it lighter, but it has significantly less wetted area and less appendage drag. That means that it's required SHP is far less than a T37, which is why a n Atomic 4 worked just fine in the Pearson. Anyway, you might be fine under most conditions but you might also want to consider whether a potentially underpowered boat will be marketable for resale.


 
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 Post subject: Re: beta marine (again)
PostPosted: 22 Mar 2021 22:25 
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Skipper

Joined: 14 Jul 2012 20:36
Posts: 495
Location: Norfolk, Va
The W50 (41hp) is over powered in the T37, and only there because they got a deal on them. The W40 (33hp) is very close to the correct engine. I know I could tell when I went down from 41hp to 35hp, but still happy. The Beta 25 has a very peaky torque curve, needs to run 2,400-2,600 RPM, at that RPM it's only making 18hp. Pushing my T37 with a clean bottom at my avg cruise 6.3kts @ 2,000, we're making 27hp. I think the 25hp for dropping a mooring ball and going out for a daysail/weekend would be fine. If you're planning to use it to push into 6ft seas making your way down the thorny path, it isn't the right motor. It is nice to have the power when you need it. The first time I ran aground with the B35, was surprised it didn't have as much ass as the W50 to push off or the first time powering thru an inlet. Remember if you're pulling a 100 amps off the engine, you'll be losing a couple hp right there. The smaller motor has a lot of good going for it, weight, space and cost, just not sure it's enough motor,

_________________
Hull #208, Puff Card
Southern Chesapeake Bay


 
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 Post subject: Re: beta marine (again)
PostPosted: 23 Mar 2021 07:06 
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Skipper

Joined: 09 Aug 2017 15:35
Posts: 725
Location: Maine/USVI
Thank you. That all makes great sense. I have a feeling I will need to re-prop no matter what I do unless I simply do a head job on the Westerbeke, replace the heat exchanger and run from there. If I'm going to get a reman Cummins 6BT into the other boat that may be exactly what I have to do. So what I REALLY have to do is stop watching running Beta videos on youtube.


 
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 Post subject: Re: beta marine (again)
PostPosted: 26 Mar 2021 22:15 
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Skipper

Joined: 29 Dec 2006 09:38
Posts: 656
I always thought my W50 was too large and have no idea why I put a Yanmar 3JH 39 hp in it, but it has been fine and I have appreciated the ability to power through those square 5 footers that stop most boats. I run at 80% most of the time and the boat seems to warm up fine and be happy with its load. Seems to me that once you cross the bridge of having "enough" power there, the big issue is getting it through your prop and matching up the variables to a pitch. That is where an externally adjustable prop (mine is an Auto-stream sold by Martec. I am not sure how much lighter the Yanmar is over the W50 but it is some as I can tell and I really think I like the motion of the boat better with the weight in back. This is a 20K # boat (at least no matter what the brochure says) and in is not a surfing sled on its bottom. Comfort offshore matters.
My winter boat (I live in California in the winter) is an Ericson 32-200 with a Universal (Kubota) 25 hp. I have a hard time envisioning that engine comfortably driving my Tartan. They are very different boats and I have a crappy Campbell Sailor two blade so I am not comparing apples to apples, but it just does not seem to have the depth that would make feel comfortable. I am trying understand how a serp would take more out of the engine. Seems to me the substantial reduction in bearing tension and friction would reduce all the drag overall.
Ray Durkee


 
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 Post subject: Re: beta marine (again)
PostPosted: 28 Mar 2021 06:56 
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Tactictian

Joined: 06 Aug 2020 09:02
Posts: 142
Velara, my statement about a serpentine belt taking more from the engine is based on the presumption that it would allow a higher load from the alternator. I just installed a 105A alternator but I'm using the standard 3/8" belt. No way I'm getting anything close to 105A out of it and I'll need to use the belt load manager to de-tune the alternator to maybe 70A. So, 35A x 14V = 420W which is a bit more than 1/2hp.


 
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