How much horsepower??

[geoleo]

Originally Posted by a64pilot

His point is to size an engine according to its use, don’t put a 100 HP engine in when and if a 20 is all that’s needed. It will among other things burn more fuel, it will also be heavier and larger, use more oil and most likely its parts will cost more too, and likely because it’s shoe horned in may be a real bear to maintain.

Actually he’s saying he wishes he had more than 115 I guess.

Ok -but that does not really relate to my post-- I was lamenting way undersized engines put in 80 s and 90 s production sailboats

[geoleo]

Originally Posted by a64pilot

His point is to size an engine according to its use, don’t put a 100 HP engine in when and if a 20 is all that’s needed. It will among other things burn more fuel, it will also be heavier and larger, use more oil and most likely its parts will cost more too, and likely because it’s shoe horned in may be a real bear to maintain.

Actually he’s saying he wishes he had more than 115 I guess.

Well in my 1965 wood Garden 10 ton 35 ketch I replaced the original perkins 4-107 with a Yanmar QM30F driving a 15X15 3 blade prop and it was perfect! Could maintain a good speed blasting thru a 3-4 ft chop. I even blasted the ornamental carved trailboard off one time. Mounted the other trailboard on the garage wall.

[a64pilot]

Originally Posted by geoleo

Ok -but that does not really relate to my post-- I was lamenting way undersized engines put in 80 s and 90 s production sailboats

That’s the thing, they aren’t way undersized to most, they are just fine.
But many don’t seem to be in as much of a hurry, and I’d suspect those people may sail more too, as opposed to cranking her up and pushing past hull speed.
If your in a hurry, fly.

[john61ct]

That's why I reco'd a MacGregor 26. Pretty fast powerboat poorly disguised as a sailboat, I'd think perfect for the OP.

[GordMay]

Originally Posted by HankOnthewater

I noted that up-thread it was said: 4 to 5 HP per ton displacement. Does that mean that the old rule of 3 HP per ton is not valid anymore? ...

Westerbeke Corporation suggests 2 hp for every 1,000 lb of displacement for coastal cruising, and 2.5 hp per 1,000 lb of displacement for offshore.
In their book "The Gougeon Brothers on Boat Construction" the authors suggest a good rule-of-thumb is 1 hp for every 500 lb of displacement.
Francis Kinney in "Skene's Elements of Yacht Design" recommends about 2.5 - 3.5 hp per ton.
According to Ted Brewer:
3-4 bhp per ton (1HP/500 - 600#) is adequate
5 bhp per ton (1HP/400#) is ample
6 bhp per ton (1HP/300#) is often too much.
Some people suggest 1 hp for every ft. of boat waterline length.
Some people suggest 3 - 5 hp (continuous rating) per long ton.
They’re all just Rules Of Thumb.
We’ve been endlessly discussing this topic, at least since 2005. ☞ http://www.cruisersforum.com/forums/....html#post8228

[thomm225]

Similar to the post above, most reviewers etc recommend 2 hp per 1000 lbs of displacement for offshore cruising/sailing

This from The Mahina Expeditions Site

Engine

Being able to maintain at least six knots under power will get you in most passes and channels at the time of least current. A rule of thumb is two horsepower per thousand pounds of displacement for a sufficiently powered cruising sailboat. Purists may say that this is excessive, but in my experience it has been an advantage to have sufficient power to deal with currents and the ability to motorsail to windward for short distances into steep chop when necessary.

The link to the site is: Mahina Expeditions - Selecting A Boat for Offshore Cruising

Another article by Don Casey suggest the same (2 hp/1000 lbs disp)

https://goodoldboat.com/repowering-part-1-don-casey/

from the link above:

In our case, the 2-horsepower rule yielded 24 horsepower, but I already knew that 20 would push us along smartly in smooth water

Btw, I use a 5hp outboard on my 6600 lb Bristol 27 which is less than 1 hp / 1000 lb displacement

[KTP]

If you want a big motor for going in 3 foot chop, I agree, buy a powerboat. They come with 1, sometimes 2 motors in up to 300hp.

[Nicholson58]

Originally Posted by geoleo

Ok -but that does not really relate to my post-- I was lamenting way undersized engines put in 80 s and 90 s production sailboats

I was agreeing with you. My mid 80s boat has an engine undersized. Even with the ability to optimize the prop pitch and rpm we are unable to get close to hull speed when it’s needed most. In a squall we could be pushed backwards while watching the temperature climb.

I agree that it depends on the end use. Probably over 95% of boats are Sunday sailed. The builders are selling to the crowd. That makes it rare to find a boat powered for offshore use.

[Dockhead]

Originally Posted by a64pilot

That’s the thing, they aren’t way undersized to most, they are just fine.
But many don’t seem to be in as much of a hurry, and I’d suspect those people may sail more too, as opposed to cranking her up and pushing past hull speed.
If your in a hurry, fly.

Pushing past hull speed with the motor, in a displacement hull sailboat, is a fool's errand. I don't think anyone tries to do this no matter how large the engine.


The reason for having a large engine in a displacement hull sailboat is to be able break through head seas when trying to bash upwind in bad conditions. For this you may well need more than 5hp per tonne -- if you want this capability. Plan "A" for most of us, in bad conditions when you need to get right upwind, is not to go and wait for better weather. That's what I normally do. But there are different situations where you might desire to have this option, even if it costs a lot in fuel. It happens to me from time to time, and so it's part of my dream (maybe fantasy) specification for my dream rugged, go-anywhere, high latitude boat, is that it will have a powerful engine (maybe even 6 or 7 hp/long ton) and large tankage (maybe a couple of tonnes), in addition to excellent sailing qualities.



From 150hp you can use a Hundested variable pitch prop, too -- a good reason right there to have a larger engine.

[Nicholson58]

My Hundested, 24”, 115 hp. Variable pitch from the cockpit. These are great tools.

[Dockhead]

Originally Posted by Nicholson58

My Hundested, 24”, 115 hp. Variable pitch from the cockpit. These are great tools.

My dream prop


They don't make them that small any more, AFAIK. Minimum 150hp and 29.5"

[a64pilot]

Originally Posted by Nicholson58

I was agreeing with you. My mid 80s boat has an engine undersized. Even with the ability to optimize the prop pitch and rpm we are unable to get close to hull speed when it’s needed most. In a squall we could be pushed backwards while watching the temperature climb.



I agree that it depends on the end use. Probably over 95% of boats are Sunday sailed. The builders are selling to the crowd. That makes it rare to find a boat powered for offshore use.

You should be able to run at full throttle and continuous rated RPM indefinitely without coming close to overheating.
It would seem you have a cooling problem.

Someone said they are selling to the masses, and I agree. People who look at boats or anything else love spec sheets to compare, oh look honey brand x has a bigger motor than brand y, therefore it must be a better boat, let’s buy brand x.

That is why production boats of the 21st Century have bigger motors than they did in the 1980’s, it’s not that they are superior boats.
Bigger motors sell, and I’d bet don’t cost a builder that much more, a 2 liter 4 cyl Diesel has the same number of parts that a 3 liter 4 cyl Diesel does, it’s manufacturing costs are almost the same.
Of course engine manufacturers have always priced by the HP, but we don’t know what OEM pricing is.
You may sometimes be surprised at OEM pricing, it may be good business to sell motors to manufacturers at cost or even a loss.

It was late 1980’s I think and we were offshore in a 45’ Sportfisherman, off of Tampa Bay, and were hit with quite a storm squall, and were being pushed back toward the Shipping channel which has some shallows on both sides even way out. It wasn’t that we didn’t have enough HP, it was that when your burying the bow deeply and then slamming, you just can’t push any harder without breaking something, so there is weather that you just have it fall off and take another heading.

I just don’t buy into the theory that 40 years ago boats were underpowered, just that they have bigger motors now.


Just read the first paragraph of this article, it doesn’t mean that cars of the 1980’s were underpowered, they performed their functions fine, but it does mean that power sells.
https://www.nrcan.gc.ca/sites/www.nr...tsheet_7_e.pdf

[noelex 77]

Originally Posted by Dockhead

From 150hp you can use a Hundested variable pitch prop, too -- a good reason right there to have a larger engine.

I sailed on a 43 foot yacht that was equipped with a Hundested variable pitch prop with a Yanmar 75hp engine, so they must be available for smaller engines. The owner was very mechanically capable (he built the yacht himself) so perhaps he machined some custom parts to make this option work.

For what it was worth, his view was that the cost and complexity of variable pitch prop was not justified for the small gains.

I also know of an owner of a steel 50 foot yacht who loved his variable pitch prop (unknown brand, I think probably home made). The yacht had a long keel and would not have backed in a straight line, but he found he could induce prop walk in either direction, which is an advantage I had never considered, although I am not sure it is possible to alter the pitch enough to achieve this aim with commercial props.

[Panope]

Originally Posted by Dockhead

My dream prop


They don't make them that small any more, AFAIK. Minimum 150hp and 29.5"

Nothing wrong with having an oversized prop. In fact, I would say an oversized propeller is desirable (disregarding increased sailing drag).

After upgrading from 15 horsepower with 13 inch prop to 40 horsepower with 18 inch prop, I have concluded that most of the increase in performance that I EXPERIENCE, resulted from the propeller upgrade NOT the larger engine. How do I know this? Because with both powerplants, I generally use the same amount of power (10 HP), but the larger prop gives much more performance.

I do love having the larger engine, but if I were to do it all over again, I would buy a smaller (30 HP) engine with a very high gear ratio (slow turning shaft) and an even larger propeller (20 inch).

A feathering/folding prop would be mandatory if any sort of sailing performance is required.

My boat weighs 15,000 pounds.

Steve

[geoleo]

Originally Posted by Nicholson58

I was agreeing with you. My mid 80s boat has an engine undersized. Even with the ability to optimize the prop pitch and rpm we are unable to get close to hull speed when it’s needed most. In a squall we could be pushed backwards while watching the temperature climb.

I agree that it depends on the end use. Probably over 95% of boats are Sunday sailed. The builders are selling to the crowd. That makes it rare to find a boat powered for offshore use.

The "Builders" are cutting costs every which way they can to the mostly 'stupid ' crowd.