Engines: Old and easy to repair vs New and reliable.

[Jim Cate]

The 36 footer was designed at 24,000 lbs of which 6000 lbs is ballast, an extremely high percentage even for a sailboat.

While I agree with much of what you have said, the above is not correct. A 25% ballast to displacement ratio is rather low, not extremely high. Many CCA era yachts have ~50% and most more modern production boats hover around the low 30% region.

Jim

[mvweebles]

I stand corrected. 30% is a more typical number.

Recreational displacement trawlers such as nordhavn and kadey krogen, rarely crest 10%. And these are much taller boats. Nothing wrong with them, just stating the design parameters.

Originally Posted by Jim Cate

While I agree with much of what you have said, the above is not correct. A 25% ballast to displacement ratio is rather low, not extremely high. Many CCA era yachts have ~50% and most more modern production boats hover around the low 30% region.

Jim

[Compass790]

[QUOTE=GoneDiving;3074337]

Originally Posted by mvweebles

Thanks for that. Very informative.

So what's the down side to having a low powered cruiser (say <100hp in a 25t 50 footer) in which the captain has no intention of exceeding say 7 knots:

Not maintaining forward passage in strong currents (wait it out)?
Insufficient power in rough seas?

What have I missed?

Yes thats exactly the issue with low power.
To go back to my example of the 64ft motor-sailer with the 75hp Cat, from memory, it would do 8knts ( cruising) in flat water with no wind but against say 25-30knts & a 4 metre swell it would be down to 1.5knts.
This is approximate from memory but the principle applies.

Waiting it out is an option, if you have the sea room you can lie to a sea -anchor.

It sounds like you have a good handle on the compromises you need to make.

In our current sailboat, a 26ft sloop, we only have an 8hp engine & it has caused some hairy moments because of it's lack of power trying to get out of open anchorages when there is an unexpected wind change. Have been forced to motorsail with a storm jib to get out.

But yes you need people with the size boat & powerplant you are considering to chime in with their experiences

[mvweebles]

[QUOTE=Compass790;3075344]

Originally Posted by GoneDiving

Yes thats exactly the issue with low power.
To go back to my example of the 64ft motor-sailer with the 75hp Cat, from memory, it would do 8knts ( cruising) in flat water with no wind but against say 25-30knts & a 4 metre swell it would be down to 1.5knts.
This is approximate from memory but the principle applies.

Waiting it out is an option, if you have the sea room you can lie to a sea -anchor.

It sounds like you have a good handle on the compromises you need to make.

In our current sailboat, a 26ft sloop, we only have an 8hp engine & it has caused some hairy moments because of it's lack of power trying to get out of open anchorages when there is an unexpected wind change. Have been forced to motorsail with a storm jib to get out.

But yes you need people with the size boat & powerplant you are considering to chime in with their experiences

I too have been on a couple sailboats that were woefully underpowered. I remember a Dreadnought 32 that had some miniscule engine (lister?) with a variable speed prop. It was totally vulnerable and unmaneuverable in anything other than bathtub flat waters.

I took the question to mean lower end of power range, not under powered. The boat should be able to maintain hull speed (say, 1.1 or 1.2 sr/wl) in reasonable and normal operating conditions. If 15-20 kts of headwind in otherwise flat water will prevent you from maintaining hull speed, you're under powered. Assumes your prop is relatively efficient and hasn't been compromised for sailing efficiency.

[GoneDiving]

Originally Posted by mvweebles

I took the question to mean lower end of power range, not under powered. The boat should be able to maintain hull speed (say, 1.1 or 1.2 sr/wl) in reasonable and normal operating conditions. If 15-20 kts of headwind in otherwise flat water will prevent you from maintaining hull speed, you're under powered. Assumes your prop is relatively efficient and hasn't been compromised for sailing efficiency.

Boating seems to be full of rules of thumb. Is there on for approximate hp requirements for a non sailing displacement vessel operating in the real world?

I'm assuming calculators also only allow for ideal conditions. Using one, I got 29hp for our hypothetical 25t 50 footer to do 6kn and 100hp to achieve hull speed of 9kn.

Every vessel being able to achieve hull speed in calm water seems like a realistic expectation to me, especially if it gives a 300% safety factor on the power required for the intended cruise speed.

Cheers.

[skipperpete]

Nope, no rule of thumb. Cruising sailboats tend to observe the hull speed as the HP limiting factor as well as tank capacity and consequent endurance but motor cruisers are gloriously free of these constraints. Endurance is less of an issue because they are mostly coastal craft and rarely cross oceans. Hull form allows huge fuel tanks and underwater shape allows semi planing. For instance the Apreamare24 is fitted with 2 turbocharged 4LHA Yanmar’s with shaft drive and a speed of 25 knots from 600 hp and the same boat in the 40 ‘ version has two 600 hp Volvo’s. The Nordhavn’s use a naturally aspirated 6 cylinder Lugger engine based on a John Deere industrial unit of maybe <200 hp that gets it along perfectly well across oceans economically. Super yachts use enormous amounts of HP both for the main propulsion units as well as the generators and often bunker 200,000 litres of diesel fuel.

[GoneDiving]

Originally Posted by skipperpete

. Endurance is less of an issue because they are mostly coastal craft and rarely cross oceans. Hull form allows huge fuel tanks and underwater shape allows semi planing.

I'm looking for something that's capable of crossing oceans as I want to be able to get to the remote diving destinations so that's why I'm trying to balance reliability, safety and range. Very valid points were made earlier that if I select a powerful or inefficient engine then I may not even be able to get to my intended destinations.

It's actually one of the limiting aspects I'm finding with intended vessel length. I'm trying to keep it under 50ft for cost, simplicity and ease of single handing when suitable. However, it's rare to find a used sub 50 footer with >2000ltrs/600gal. Stepping above 50ft often brings 6000ltrs/1800gal but at the costs mentioned above. Unfortunately my budget doesn't run to a Nordhavn etc.

Thanks.

[MartinR]

My 5 cents. I much prefer older, reliable engines to modern electronically controlled. Also, slower turning engines are preferable to faster.

There are many good engines out there. My personal favourite is Scania, but Cummins and Cat among others make very good engines.

As for Turbos, I can see no reason to have an engine without. A turbo is not exactly a piece of High-Tech and they have been perfected long ago. The engine runs quieter and with better fuel economy. In the commercial world, where reliability is extremely important, the vast majority of engines use turbo chargers.

[Lepke]

2 stroke doesn't equal poor economy. It depends on the design. Large ship engines are 2 stroke. It's more efficient. The entire cylinder is flushed with fresh air instead of mixing the incoming charge with whatever exhaust gases remain. Flushing the cylinder with fresh air is also part of the cooling. Another reason 2 cycles last a long time. And every stroke provides power.

Detroits tale of poor mileage comes from the thousands of war surplus engines stuck in too small boats with the wrong prop because they were cheap. And from sport fishers that like to run flat out at 30 knots and then cry about the fuel usage. My current 1947 engines burn about 4.25 gph each at mac continuous when the book says 6 gph. Somebody before me got the props and hull right and I tuned the engines.

[mvweebles]

Originally Posted by GoneDiving

I'm looking for something that's capable of crossing oceans as I want to be able to get to the remote diving destinations so that's why I'm trying to balance reliability, safety and range. Very valid points were made earlier that if I select a powerful or inefficient engine then I may not even be able to get to my intended destinations.

It's actually one of the limiting aspects I'm finding with intended vessel length. I'm trying to keep it under 50ft for cost, simplicity and ease of single handing when suitable. However, it's rare to find a used sub 50 footer with >2000ltrs/600gal. Stepping above 50ft often brings 6000ltrs/1800gal but at the costs mentioned above. Unfortunately my budget doesn't run to a Nordhavn etc.

Thanks.

Guessing your budget has a "1" as the first digit. Not sure I'd cross an ocean in a single engine power boat unless it had some sort of auxiliary power source, so I'd probably consider some sort of one-off motorsailor if I could find one.

These older Willard 40s are simple, reliable, and relatively well built. Deck house scantlings probably won't survive Perfect Storm conditions, but neither will most sailboats. Bone up on weather and be patient with seasons.

https://www.yachtworld.com/boats/198...wler-3550716/#

[GoneDiving]

Originally Posted by mvweebles

Guessing your budget has a "1" as the first digit. Not sure I'd cross an ocean in a single engine power boat unless it had some sort of auxiliary power source, so I'd probably consider some sort of one-off motorsailor if I could find one.

These older Willard 40s are simple, reliable, and relatively well built. Deck house scantlings probably won't survive Perfect Storm conditions, but neither will most sailboats. Bone up on weather and be patient with seasons.

https://www.yachtworld.com/boats/198...wler-3550716/#

Thanks. Yes, a 1 leaves room to move and increase (which it always does 😀 )

It may be naive but I'm comfortable with a single main engine as long as it's well maintained and low stressed. I'd agree that some form of aux would be wise. Luckily there are quite a few sail stabilised/assist in the market here and yes, they are under consideration.

The recreational trawlers are great. I'm not sure why they are rare in Aus. Not unicorns but definitely not as popular as the US. Most 'trawlers' are converted commercial vessels or 500hp planing cruisers.

At this stage I'm leaning towards an old converted cray/lobster trawler with a simple but reliable drivetrain. If I stay below 50ft, it ticks a lot of boxes but I'll probably have to add additional tankage to get the range but that's not a show stopper. Mid sized vessels with lots of tankage are rare here.

Thanks again

[mvweebles]

Didn't realize you were down under.

I'm a devout single engine guy. But I worry about the stuff that isn't on a maintenance schedule. A cracked high pressure diesel line will stop you dead unless you have some sort of brazing equipment. Shaft in a transmission breaks. These may be really rare events, but being 700 nms offshore means you have to have a plan of some sort, even if the plan is no plan. There's a lot of responsibility when you head offshore - being single-threaded on a critical component requires deep thought and planning to mitigate risk as best possible.

I too have looked at converted fishing and commercial boats. 90% of the ones I've seen are not great. I knew a guy who had a 65-foot US Navy Yard Tug that was done well on the interior, but had a massively oversized engine and prop. The fishing boats I've seen have really spartan accommodations with some oddball use of the enormous fish hold. Many low quality DIY conversions. But they're out there. Many are very inexpensive.

[Mainstreet]

My Morgan 462 ketch which weighed in at close to 40,000 lbs cruise loaded was powered by a Perkins 4-236. Because cruising a sailboat is essentially moving under power 90% of the time (at least it was in our case) we put a lot of hours on that engine. Typical sweet spot was 1800 RPM resulting in 5 knots. Fuel usage about a gallon an hour. Maintenance was simple and easily accomplished with very diligent lube and transmission oil changes and a constant watch for heat exchanger failure, which didn’t happen in 2500 miles cruising I’d take that Perkins over any fancy “new electronic or supercharged engine any day.

[dalemann]

It is not the failure of an engine part that is likely to cause you problems. The real menace is the computer control systems on newer more efficient engines.

With an older engine if you give it air, fuel and cooling water it will run. Usually for thousands of hours.
If the computer controls on a newer engine act up you will have to fly in a factory tech to diagnose what could actually be a very small glitch.

[rslifkin]

Originally Posted by dalemann

If the computer controls on a newer engine act up you will have to fly in a factory tech to diagnose what could actually be a very small glitch.

Not necessarily. Some engine electronics can be diagnosed with tools that are fairly available and not insanely expensive. I'd personally base an engine choice for modern stuff on whether I can reasonably obtain and carry at least basic diagnostic tools for it.