[Repower advice] How much HP is enough? Tartan 42

[thematt]

Hey folks,


My Westerbeke W50 (3200 rpm) in my Tartan 42 (32' water line) hull speed ~7.5 kts (22K lbs dry, call it 25K loaded), has given up.


I'm looking at the following engines:
Beta 35, 43 or Yanmar 3JH40, 4JH45


There's been a ton of discussion about common rail with ECU vs. traditional mechanical injection. Honestly, I see pros and cons of each and am willing to work with either. My goal is to go offshore one day though, so call me slightly in favor of mechanical, but not enough to rule out a better fitting, quieter, more fuel efficient engine.



What I'm curious about is how much horsepower is too little. Specifically, the Beta 35 looks very ideal and torque and power curves look well matches against the w50. And I love the idea of a smaller easier to access engine, plus the fuel efficiency is inline with the more powerful yanmars I'm looking at. But is 35 just too small?



Conversly the larger Beta43 will require modifying my already cramped engine room but in every other way is superior to the W50.


The Yanmars look like they would both fit, but like I said, I'm slightly in favor of mechanical injection for my intentions, but if 35HP is just too small? I would rather go with 40 or 45HP without modifying the engineroom if possible vs greatly reducing access to the engine which would likely be the case with the beta 43.



Currently I believe I'm underproped with a flexofold 16x10-3. I have a 1.9:1 reduction transmission.



Any advice and thoughts are much appreciated. This is a huge expense for me so I want to get this right!

[Sailorman97]

I bought a Betamarine engine 2013 . 75hp.

I gave the prop guy at flex-o-fold the specs and he sent a prop and my engine could not spin it up to red line, missed by 450 rpm on a 2600 rpm motor

I had just enough time left to exchange the blades to the next size down. They came and I installed them and missed by 150 rpm. Now I was out of time and could not exchange the blades.


6 yrs later I was looking for service manual for the engine from Kubota and chanced across the Kubota power rating sticker on the motor. It was 49.8 kw which is 66 hp. No wonder I could not swing the prop.

I looked at the power curve Beta gave me and the power curve supplied by Kubota and they were not the same.


So lets look at the evidence.
Prop ( sized by the prop manufacturer) bought for motor based on specs given by Beta could not be turned to max RPM and the next size down could not be turned at max rpm either.

Conflicting specs found on motor

Now who you going to trust?


So if your considering Beta then just know that their documentation on my motor did not jive with Kubota's documentation and I was unable to turn the prop that was based on Beta's specs.

BTW, I ended up cutting 1/2 off the 3 blades to get them to turn at max rpm

[SY Harmony]

Have you considered a rebuilt 3/4JH mechanical engine?

[thematt]

Thanks for the replies folks,



@Sailorman, the 35 at least looks like the exact same specs as the engine on Kubota's website, if slightly less HP and rpm, but same displacement.



I haven't considered a rebuilt, since I don't have the time to do the repower myself, so the actual engine cost (within reason) is no too much of a factor since it's not the large part of the cost, and I like the benefit of a warranty.

[fourlyons]

OP, your question is, "is the Beta 35 too small?"

Last year I repowered my 39' keel centerboard ketch, 34' waterline, 4' draft, 22,000 pounds with a Nanni 3.75. That is a marinized 20hp Kubota, same specs as the Beta 20. I wanted a small, light engine. Everything I read, said that turning a larger prop more slowly would deliver more hp to the water as thrust. So I installed a 3:1 gear and a 16.5" three blade Autoprop. It turns out I'm a little under propped, the engine maxes out 200 rpm too high. I max out at 7.2 knots, in ideal conditions, under power. 8.5 knots under sail.

Maybe that information will help you decide about the Beta 35.

[boatpoker]

September 2022 I tried to order a Yanmar ... couldn't get a delivery date.

Ordered a Beta in September 2022, got a sort of delivery date of May 2023.

Found a 3yr old Beta still in original crate, cancelled my order with Beta and bought that.

Check out availability before you get committed to one or the other.

[thematt]

Wow awesome fourLyons, exactly the info I was looking for! I'm still learning a lot, but when I started this engine journey and learned a bit it felt like everything was overpowered in similar production boats and thought I must be missing something.



I don't need to go hull speed in chop and a strong head wind, but I don't want to be stuck either. I'd definitely be motor sailing in those conditions if need be anyway.


I have a lead on a beta 35 that's available now so I'm heavily leaning that way!

[boatpoker]

Originally Posted by thematt

Wow awesome fourLyons, exactly the info I was looking for! I'm still learning a lot, but when I started this engine journey and learned a bit it felt like everything was overpowered in similar production boats and thought I must be missing something.



I don't need to go hull speed in chop and a strong head wind, but I don't want to be stuck either. I'd definitely be motor sailing in those conditions if need be anyway.


I have a lead on a beta 35 that's available now so I'm heavily leaning that way!

I am a Beta fan but nothing is perfect. Join the Beta Owners Facebook page and search "corrosion". They do have some issues. https://www.facebook.com/groups/1724...61125133934503

Before our engine was installed I replaced a couple of stainless steel (with aluminum)brackets bolted to aluminum due to galvanic potential. I also removed almost every bolt on the engine and treated them with Tef-Gel along with some mating surfaces of dissimilar metals.

Mine is a 50 and I don't know much about the 35 but it's worth checking out.

[ABJ87]

Don’t rule out the Beta 38. Same footprint as the 35.

Talk to Beta, they where very helpful with the repower on our last boat.


We have the 38 in our T37 and it’s fantastic.

[roryboy]

Originally Posted by boatpoker

Before our engine was installed I replaced a couple of stainless steel (with aluminum)brackets bolted to aluminum due to galvanic potential.

I've seen these engines. What bracket on a Beta engine is made of stainless steel?

[maine50]

I have a Tartan 43 (1974) same hull as late 70's Tartan42. I put a Beta 38 (10 yrs ago in and recently put on a flexofold prop 17dia 12 pitch. I'm slightly overpropped as I can do 7.5 at 2600rpm. I chose the higher of the two choices that Flexofold suggested. My trans is a TW 60 w/ 2.0 I believe. Prev I had a Kiwi prop and the flexofoldis more efficient as it has shaped blades not flat feathering blades.

[tkeithlu]

QUOTE: "The Yanmars look like they would both fit,"

Realize that when you change engines, as opposed to a rebuild or replacement with the exact engine you had, you enter a world of hurt. "Fitting" is only the first problem, and it's a big one. The designer didn't waste space on the engine (or accessibility!) when he could use that space for things that sell boats at boat shows. Once over that hurdle, you find that the seacocks are all in the wrong places, because he put them in to minimize hose runs. Then the mounts are wrong, the space to the prop shaft is wrong, the control cables are wrong, the electrics are wrong, and God forbid that you should ever want to get to the oil filter.

So, consider the advantages of a rebuild or a replacement in kind. Consider spending your time/money getting the prop right. Best wishes on the success of your project.

[boatpoker]

Originally Posted by roryboy

I've seen these engines. What bracket on a Beta engine is made of stainless steel?

On our Beta 50, the bracket on which the fuel filter is mounted to the intake manifold and the bracket on which the manual oil pump were on ours. Both bolted to aluminum castings ... a galvanic soup.

[Cheechako]

Think about what RPM you wanna run. Many modern engines are rated at high rpm and thus higher HP and sound like an airplane in use. I want to know how much HP it puts out at reasonable RPM. Like 2600 etc.
Buy the HP you need at the RPM you'd rather have.... within reason.

Large commercial diesels are sold for different ratings at different RPM's.
Recreational use: maybe 3600 RPM rating
Intermittant use: maybe be 3200 RPM rating
Continuous use: may be 2600 RPM. etc.
Basically the same engine.

[thematt]

Thanks for the replies everyone and links to more info!



It's getting harder and harder to find parts for the W50 and recently had the bad luck of incountering an injector pump issue, likely head gasket failure, and an extremely pitted and leaking exhaust manifold all at once. It's for these reasons I want to repower and the general anxiety over trusting the engine to fire that these problems have caused. I know the cost is going to suck, but I just want to enjoy the boat.


All the engines I listed that I'm interested in are 2800 or 3000 rpm engines vs. The 3200 of the current W50. I wouldn't be against the beta 38 at all but I do have a newish transmission at 1.9:1, so the 3600 rpm the 38 makes would spin the prop a bit to fast or try to at least (I believe).


For the folks chiming in regarding their similar boat length and power, double thank. This is making me confident in going with the smaller 35 vs a 40-45 HP engine.