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

[thematt]

Thanks all! I'm learning a ton from this.


I spoke with my mechanic and betamarine west (I'm in the PNW). To paraphrase, they recommend the Beta 43 over the 35. While, the 35 would work for most situations, the 43 would be a great match to the hull / displacement. Only a 6 month wait on that though



I say hull, because the prop is undersized. I confirmed with the other Tartan 42 owner in the thread the max prop size is only ~17 inches. They also had said access is tough on the 4JM engine block.


I favor fuel economy and ease of maintenance over pure HP as long as I'm not crazy underpowered.


Seems like a middle ground would be a 3JM with 40HP. Of course that engine is too narrow for the stringers lol. Checked on exhaust for the yanamrs. Both need 3" and a larger raw water inlet.



The folks at betamarine west said the the prop and transmission are well matched to the 35, so perhaps I was only ever using that much power anyway.



This repower thing isn't easy and doesn't seem to have a perfect answer in my situation. I appreciate you all taking the time to chime in and help me consider things I've missed!

[BBill]

I prefer mechanical. The Beta displacement is 91 and 35 hp @ 2800. The W50 is 110 and 41 hp @ 3200. I suppose you are running the W50 at about 2400 and will be running the Beta at less than 2800? Getting hull speed in calm water isn't a good benchmark to me. If you have the right gear ratio the Beta might be close in prop thrust but... nothing replaces displacement and the Beta is giving up about 20%. If your plans are to punch though high winds and breaking inlets the larger Beta would be a better choice to me. Its easy for me to spend your money too.

[sailingharry]

I am going to caution against downsizing the engine. We have a 43 ft, 20,000 plus pound boat with a 55 horsepower. I have used all 55 horsepower on multiple occasions. Note that we are aggressively distance cruisers, covering a total of 7,000 NM over 8 months between 2021 and 22. While the boat is a wonderful sailboat and we love to sail, those kinds of distances don't allow much time for sitting around or sailing slowly. We've motored in conditions where a sail would be pleasant, and we have motored and conditions were a sail would not be pleasant!


There are several types of conditions where having all those horses are nice.
* Motoring up at or above hull speed where you have a lot of miles to cover. We had no wind as we transited the hundred plus miles between Port aux Basque NL and the Bra d'Ors In Nova Scotia. Most of that trip was above hull speed. It would have been a night time entrance if we were any slower.
* Motoring against significant current. The port of Montreal is a mile up River with over six knots of current against you.
* Motoring in unpleasant adverse see states. If you need to go up wind in really snotty conditions, sometimes motoring is preferable.
* A big one, which the EP advocates often miss, is maneuvering. When you are making a difficult landing in really bad conditions, it is really nice to make a high speed approach, knowing that you can stop the boat in half a boat length. Equally nice is putting the helm hard over and going from 0 to full throttle for 10 seconds and have the boat spin.


I wouldn't give up a single one of my 55 horses!

[thematt]

Originally Posted by BBill

I prefer mechanical. The Beta displacement is 91 and 35 hp @ 2800. The W50 is 110 and 41 hp @ 3200. I suppose you are running the W50 at about 2400 and will be running the Beta at less than 2800? Getting hull speed in calm water isn't a good benchmark to me. If you have the right gear ratio the Beta might be close in prop thrust but... nothing replaces displacement and the Beta is giving up about 20%. If your plans are to punch though high winds and breaking inlets the larger Beta would be a better choice to me. Its easy for me to spend your money too.

Ha! This is pretty much verbatim what the mechanics / beta dealers have said, that 'displacement is key'. The cost difference on the engine (beta 35 vs. 43) isn't huge. It's more aspect of lead time and fit. Both of which the beta 43 falls short sadly. Thanks for your input.

[moonmist]

This is form the Beta 35 web site. I am going to speculate that the engine is detuned to only reach 2800 rpms to met emmissions. Note the Beta 38 is the same engine turning 3600rpm. Go to https://betamarineusa.com/ the web site is a wealth of information Give Stanley a call
This engine is suitable for boats with displacement of 9-10 tons with a water line legnth (LWL) of 37-39 feet.

Horse Power35 @ 2800 rpm

4

78mm/3.07"

78.4mm/3.09"

1498cc /913 ci

170kg / 375 lbs

TMC 60

65 Ampengine is

Cylinders

Bore

Stroke

Cubic Capacity

Weight

Transmission

Alternator

35 @ 2800 rpm

4

78mm/3.07"

78.4mm/3.09"

1498cc /913 ci

170kg / 375 lbs

TMC 60

65 Amp

[roryboy]

Originally Posted by boatpoker

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.

With all due respect. You are mistaken.

[BBill]

Originally Posted by moonmist

This is form the Beta 35 web site. I am going to speculate that the engine is detuned to only reach 2800 rpms to met emmissions. Note the Beta 38 is the same engine turning 3600rpm. Go to https://betamarineusa.com/ the web site is a wealth of information Give Stanley a call
This engine is suitable for boats with displacement of 9-10 tons with a water line legnth (LWL) of 37-39 feet.

Horse Power35 @ 2800 rpm

4

78mm/3.07"

78.4mm/3.09"

1498cc /913 ci

170kg / 375 lbs

TMC 60

65 Ampengine is

Cylinders

Bore

Stroke

Cubic Capacity

Weight

Transmission

Alternator

35 @ 2800 rpm

4

78mm/3.07"

78.4mm/3.09"

1498cc /913 ci

170kg / 375 lbs

TMC 60

65 Amp

Very interesting. The Beta brochure shows two different hp ratings at 2800 rpm. EU compliance is about 10 hp more at 35 hp...so this explains the smaller displacement. For practical purposes it appears the Beta 35 is closer to USA compliance rating and 25 hp. That tells me the Beta 35 is too small.

As stated already, call Stanley. I communicated with him yrs ago for a repower. He is a wealth of knowledge which also includes past repowers/performance on many different boats. Regardless, I would go Beta.

[thematt]

Update: Thanks all for your recommendations. Advice and input.

Ultimately I've decided to go with the Yanmar 4JH45, next up better suited prop (I'll probably stick with flexofold) and a beefed up fuel filtration.

[Icarus]

Originally Posted by 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!

More important is the torque curve...
Not much good having an engine hammering away at 3500 rpm reach peak hp.
My 12t 40 ketch reaches hull speed at 1900 RPM at 27 hp....around 6.5 kn.

[rslifkin]

Originally Posted by Icarus

More important is the torque curve...
Not much good having an engine hammering away at 3500 rpm reach peak hp.
My 12t 40 ketch reaches hull speed at 1900 RPM at 27 hp....around 6.5 kn.

As long as the gearing and prop are selected to match the power curve of the engine, it doesn't matter what RPM is needed for full power. It'll still do the same job of pushing the boat. But a higher revving engine of equipment power will just need a deeper reduction gear to get a suitable prop RPM for the application.