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

[drgtmartin]

Yes, I think there were only 34 Tartan 42's made. I had hull #29 for about 10 years and sold her about a year ago and she went to Warwick, RI.

The only modification that had to be made was to the engine beds. No surprise the old W50 engine shaft did not line up with the Yanmar, so the engine beds needed to be shaved down by a couple of inches. All this work was done by Dion in Salem, MA who did a very professional job.

It should be noted that the Yanmar specifications required a larger raw water intake to be installed. When the engine installation was first completed and checked for compliance to Yanmar specifications, it was found that the back pressure on the wet exhaust was too high. This was in part due to the long exhaust tube out of the boat. To comply with Yanmar and validate the warranty, a dry exhaust/water separator was installed to reduce exhaust pressure. Never had a problem with it.

With the repower, I bought a new hurth transmission and had the Walters V drive rebuilt.

I think the dimensions on the 4JH57 were close to the W50. But Dion did have to remount the companionway stairs to pull then forward by an inch or two to accommodate the mixing elbow under the stairs.

[maine50]

Be sure to check exhaust hose requirements for the Yanmar. might need to upsize from the w50 esp if you have a long run.

[IoannisD]

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!

Generally, a stronger engine will help when the winds are not favourable, so if you can afford it I would recommend it. Re ECU, I have a 4JH80 on my Finnsailer 35, admittedly a motorsailor, and had no problems - very quiet, very economical (about 3-4 Lt/hour at 2,000 rpm making 6-7 kn without sails - genoa adds another knot), hope it will be reliable in the long run, no issues yet ;-) - bought new in Greece in 2021 at around 12,500 Euro with ZF and C35 panel. It appears to be the same size as the 4JH45 by the way...

[AJ_n_Audrey]

I re-powered last year from Westerbeke 40 to Beta 35. The Beta is definitely more powerful than the Westerbeke, quieter, smoother, and more fuel efficient. I have a 17 inch MaxProp which moves the boat along about 3/4 to one knot faster than the Westerbeke did - I can do 6 knots while burning only about 0.7 gallons per hour. The smaller engine is great for access - the westerbeke access just sucked. I've made several calls to the tech help line at Beta, and I've been very happy with the support. My boat weighs about 19,000 pounds (Pearson 367), is 30 feet at the waterline and 36.4 feet on deck.

I'm very happy with the Beta. If you are serious about Yanmar, make sure it will fit on the rails in your boat. Yanmars are also great engines, as long as they fit.

[Wolfhound]

We had a Beta 35 that powered our Allied Seabreeze 35 into head-on 45 knot winds & 12-foot waves on one occasion, and 50 knots & 14-foot on another. These were steep, closely-spaced Lake Michigan waves, and we did 4 to 5 knots. The Beta 35 is a great, well-designed engine with affordable parts that are available along with good NC backup.

Wolfhound

[merrydolphin]

Originally Posted by 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.

OK folks PAY ATTENTION TO THIS GUYS POST! Reduction gear is the overlooked factor! He is right. 2,5-3:1 reduction with larger prop will give you MUCH more motoring ability. Simple physics, it’s less slippage. In if your going to cruise and not just day sail. And you are not a “purist” and most of us are not, as soon as you start to get headed with wind and sea, the standard aux sailboat powering situation goes down hill quickly. Lots of RPM on a smaller prop. Fine for a planing power boat, bad for a displacement boat. My Cal ll-46 had a near 3:1 reduction with an 85 HP Perkins 4-236 could mother like a trawler. Invaluable in many cruising scenarios. While doing the infamous BAJA BASH, nearly a thousand miles up the pacific coast of Baja Mexico most cruising boats really suffer trying to bash against 20-30 kts of wind and current in steep large seas. I have made this trip several times in different boats. Doing in my Cal was a completely different story. Take the sails down, point directly up wind and on course, put the pedal down and make good 5kts where most similar boats would be doing 1 or 2 kts or maybe even going backwards. We were swinging a fixed 26.5” 3 blade. And yes, we have sail 200 miles days under pure sail. So she could sail. Yes a good feathering prop would even be better. But it never bothered me enough to spend the money or the maintenance and bother.

Reduction gear and prop size is just not being addressed by manufactures/architects as it should be for a serious cruising boat. We also carried 260 gallons of diesel and could easily punch through the doldrums. What’s wrong with that. Many of these boats have circumnavigated. Reduction gear, prop size, greatly reduced slippage. ( you do need the room to swing a larger prop. Come on manufacturers.

[rslifkin]

As others have said, a bigger, slower turning prop will deliver better thrust at low boat speeds from an equivalent HP engine. That's a big advantage for maneuvering and motoring in rough conditions. It won't necessarily deliver a higher top speed in calm water though, and depending on the setups being compared and how much HP you have, it may actually be slightly slower in terms of top speed.

[MJH]

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!

If you have thoughts of offshore then get the larger engine for those times you will need the extra push due to weather.

Regarding your transmission that you don't mention replacing. My boat also has a 1.91 ratio, a Velvet Drive. After installing a MaxProp I was told by the transmission dealer that most boats with feathering/folding props like ratios in the 2.2 - 2.7 range. I suggest you research either having the old one upgraded to that range or replace the transmission as well during the job. Unfortunately, I checked with my transmission dealer about mine and it cannot be upgraded.

Good Luck.

[nofacey]

For 90% of it’s useage, 35hp will do fine for your hull
- but when you’re battling your way into winds and waves trying make the safe harbour before dark, or trying to get thru a narrow tortuous pass into a coral atoll with any adversity - you’ll miss that extra hp.

Answer depends on your comfort zone & future useage

[thematt]

Thanks for all the replies folks.



Regarding transmission, I believe the tranmission is new ish compared to the other gear hence I was hoping to save a bit of $, ultimately though I will go with what is optimal and do it once.


I can confirm the reduction is 1.9 and in looking at engines I'm interested in RPMs that ratio seems suitable for the rpm at the prop.



I don't believe I have the clearance to swing anything 'oversized'. 17-18" may be the largest. I'm kicking myself for not having better photos.



I don't know why folding/feathering prop manufacteres would specify a reduction ratio. Wouldn't the primary thing be prop rpm from their standpoint? Then everything falls in depending on your engine and then the reduction you need?


E.g. the beta 38, I would absolutely need a higher reduction, as engine rpm peaks at 3600. Where as the 43 or 35 the rpm is at 2800 and 1.9:1 might be great (assuming I can't fit a massive prop)


Adding to that point. Isn't there loss in prop weight to consider? Sure more blade = more work, but swing a heavy mass around has gotta impact performance at some point.

[MJH]

Originally Posted by thematt

Thanks for all the replies folks.

Regarding transmission, I believe the tranmission is new ish compared to the other gear hence I was hoping to save a bit of $, ultimately though I will go with what is optimal and do it once.

I can confirm the reduction is 1.9 and in looking at engines I'm interested in RPMs that ratio seems suitable for the rpm at the prop.

I don't believe I have the clearance to swing anything 'oversized'. 17-18" may be the largest. I'm kicking myself for not having better photos.

I don't know why folding/feathering prop manufacteres would specify a reduction ratio. Wouldn't the primary thing be prop rpm from their standpoint? Then everything falls in depending on your engine and then the reduction you need?

E.g. the beta 38, I would absolutely need a higher reduction, as engine rpm peaks at 3600. Where as the 43 or 35 the rpm is at 2800 and 1.9:1 might be great (assuming I can't fit a massive prop)

Adding to that point. Isn't there loss in prop weight to consider? Sure more blade = more work, but swing a heavy mass around has gotta impact performance at some point.

#38 Followup
From my experience the ideal drivetrain combination of engine, transmission, and prop appears to be difficult to identify clearly beforehand and ends up being a try-and-test activity. The final test is being able to run the engine at wide-open throttle (WOT) with the engine coming close (within 200RPM) to the engine manufacturer's max RPM and the prop not cavitating. Considering the entire drivetrain, while it is easier and less costly to change/adjust the prop most prop adjustment ranges are rather coarse rather than fine.

In my case the initial 18" MaxProp install resulted in prop cavitation leading to the prop being cut down an inch to 17" and prop setting changed at the next haul out. Afterwards operating about 200RPM short of WOT...the prop manufacturer (PYI) said to stop there.

FWIW the original 3-blade fixed prop was a Michigan RH18-10 and operated fine.

Good Luck.

[rslifkin]

Transmission ratio goes hand in hand with prop diameter (and max engine RPM). Assuming an engine that makes 40hp at 3200 RPM and a max speed under power of 7.5 kts, the 1.9:1 reduction and 17" prop diameter match up just fine. The ideal prop will depend a bit on the exact power output and engine RPM, but 17 - 18" diameter is right in range.



So unless you put in a much higher revving engine, the existing reduction gearing should be fine. Without the ability to run a bigger diameter prop, you might gain a little bit from a lower reduction gear (and a prop with more pitch), but it wouldn't be any large gain.

[Lee Jerry]

Originally Posted by merrydolphin

OK folks PAY ATTENTION TO THIS GUYS POST! Reduction gear is the overlooked factor! He is right. 2,5-3:1 reduction with larger prop will give you MUCH more motoring ability. Simple physics, it’s less slippage. In if your going to cruise and not just day sail. And you are not a “purist” and most of us are not, as soon as you start to get headed with wind and sea, the standard aux sailboat powering situation goes down hill quickly. Lots of RPM on a smaller prop. Fine for a planing power boat, bad for a displacement boat. My Cal ll-46 had a near 3:1 reduction with an 85 HP Perkins 4-236 could mother like a trawler. Invaluable in many cruising scenarios. While doing the infamous BAJA BASH, nearly a thousand miles up the pacific coast of Baja Mexico most cruising boats really suffer trying to bash against 20-30 kts of wind and current in steep large seas. I have made this trip several times in different boats. Doing in my Cal was a completely different story. Take the sails down, point directly up wind and on course, put the pedal down and make good 5kts where most similar boats would be doing 1 or 2 kts or maybe even going backwards. We were swinging a fixed 26.5” 3 blade. And yes, we have sail 200 miles days under pure sail. So she could sail. Yes a good feathering prop would even be better. But it never bothered me enough to spend the money or the maintenance and bother.

Reduction gear and prop size is just not being addressed by manufactures/architects as it should be for a serious cruising boat. We also carried 260 gallons of diesel and could easily punch through the doldrums. What’s wrong with that. Many of these boats have circumnavigated. Reduction gear, prop size, greatly reduced slippage. ( you do need the room to swing a larger prop. Come on manufacturers.

I'm going to try to limit my comments to a few general issues, and not get into the weeds:

1. Higher reduction gear isn't better (could be better or worse or, most probably, just different). The engine/gear/prop are a system and have to work together in balance.

2. We had the same Perkins engine in our 52 ft Tayana. It sounds like you were just on the high end of the installed power range in your 46, and liked it. That is the biggest (only?) takeaway for the OP from your entire post. I don't recall ever feeling underpowered and actually don't know how well we would have motored in those conditions (probably should have tried just to be informed, but not hours on end) because that leads me into...

3. Unless you had some kind of malfunction, why in the world are you not sailing in 20-30 kt? Way more comfortable than motoring.

4. Feathering / folding props primary advantage is reduced drag under sail; very rarely will they have a better forward performance than a (proper) fixed blade prop. (Some can actually have better reverse performance, though.)

5. Manufacturers usually fit 2-blade props that maximize calm water speed, so they can boast in brochures and at boat shows. Just like the rest of the boat, they don't outfit for real life.

[moonmist]

Not sure where you are located. STANLEY FEIGENBAUM at Beta Marine US is the most knowledgeable Beta person in the US. I installed a Beta 25 in my Pretorien 35 about 15,000 pounds. I brought it thru Sound Marine in Conn. great guy assessable, I did the install myself. Joe DeMers of Sound also strongly recommended the 25 for my boat. Used for just 1/2 season I am very happy. You call either of these two and pick their brain free of charge. I have the saildrive with autoprop. Feel free to reach out to me. Good luck

[Lee Jerry]

Originally Posted by thematt

Thanks for all the replies folks.



Regarding transmission, I believe the tranmission is new ish compared to the other gear hence I was hoping to save a bit of $, ultimately though I will go with what is optimal and do it once.


I can confirm the reduction is 1.9 and in looking at engines I'm interested in RPMs that ratio seems suitable for the rpm at the prop.



I don't believe I have the clearance to swing anything 'oversized'. 17-18" may be the largest. I'm kicking myself for not having better photos.



I don't know why folding/feathering prop manufacteres would specify a reduction ratio. Wouldn't the primary thing be prop rpm from their standpoint? Then everything falls in depending on your engine and then the reduction you need?

They don't necessarily specify, but need to know what it is. While we generally talk about HP, they are more interested in torque - the torque required by the prop has to equal the torque delivered by the engine through the trans. (Yes, torque and HP are related...) They don't ask for it because they get the data from the engine manufacturer. It's the propeller that determines the operating rpm, not the engine. Or more precisely, the propeller (and boatspeed) is determining where within the engine map the operating point is. So their job is to match the propeller pitch, diameter, number of blades and other factors for the engine to operate "in the zone" while meeting your requirements (size limits, preferred operating point, etc.).

My two recommendations for you are:

1. Talk (or submit your specs online) to some prop providers before you choose the new engine. They will want your info (displacement, engine make / model, HP, etc.) and then tell you what prop they recommend OR IF THEY SEE A MATCH ISSUE (maybe requiring a different trans or more power). You can discuss as necessary the various engines and trans.

2. If interested in more details, pick up a copy of The Propeller Handbook by Dave Gerr. (Rhymes with bear.) Maybe more than you're looking for, but for $20 or so bucks (compared to how many 1000s your about to invest) might be useful.

E.g. the beta 38, I would absolutely need a higher reduction, as engine rpm peaks at 3600. Where as the 43 or 35 the rpm is at 2800 and 1.9:1 might be great (assuming I can't fit a massive prop)


Adding to that point. Isn't there loss in prop weight to consider? Sure more blade = more work, but swing a heavy mass around has gotta impact performance at some point.

I don't think the mass is particularly material compared to the hydro forces on the blades. The other characteristics are way more important.