Efficient Powerboats vs Efficient Sailboats (Running Cost Comparison)

[Alchemist]

There is a guy here in NZ building a tri to be powered by twin 115 4 stroke outboards that he intends to cruise the pacific in it. Very cheap horse power compared to inboard diesels. Needs a tri to support the motors i guess. This thing looks similar to the earth race boat

[cat man do]

Beau, one of the members on here is talking about building an alloy outboard powered motor tri that'll break down to fit in a 40 foot container

Nothing like the Craig Loomes device





Craig Loomes Design Group


but an interesting hull concept and idea anyway.

He should be building soon i'd reckon.

Click on the above pic and check out the steering posi, and tell me how you are supossed to see out of the window's.

Dave

[Wilverine]

I like the idea and convenience of power but the trick is How to use it. On most weekends I spend more in ice than I do gas!

[Tnflakbait]

I think that an good power cat is a very nice efficient setup, but I would like to have the mast on there just in case. It doesn't hurt it too much. Say you are headed downwind for a 500 mile stretch. It would be a shame not to be able to sail if the wind was up. But that is just personal taste, and I don't own a powerboat. However I do think a well design sailing cat can be a great balance between a power and a sailboat.

If a cat sails well it can motor well. My 33' cat has a 30 hp outboard. It motors at a top speed of 11 knots. That is really good speed for a "sailboat" Of course I cruise at 7.5 to 8.

[OldYachtie]

Since most sailboats are also powerboats, the distinction isn't that clear. If you want a roomy, fast powerboat, you are going to pay for it. People going offshore on pure powerboats are quite careful about keeping their engines in good shape, and pay lots of money for fuel polishing systems, "get home" drives, etc. See The Trawlers-and-Trawlering Archives .

If you are going to pay for an aluminum mast, shrouds, stays, chain plates, turnbuckles, tangs, slides, tracks, sails made by sail makers, winches, roller furlers, etc., you are going to pay a lot for a rig-probably more than you pay to install an diesel inboard auxiliary engine. Of course, if you dispense with those things, you won't pay much for a rig.

I sailed from Seattle to Hong Kong with a 34' boat with grown wood sticks, and didn't pay for any of the above except for sail maker made sails. Next time, I won't even have sail maker made sails, and I'd pit my boat against any cruising ketch of the same size for performance with no fears. I started out in fin keel marconi sloops, and would never go back. Do boats made the way I describe have to suck? Not in my experience. See Beach Cruiser -

[spencer53]

There was a similar thread on here very recently. The original poster was the primary respondant. I think depending on use, cruising area, prevailing winds, etc..... the discussion on the other thread pretty much ended up a tit for tat. Some say power, some say sail. The most important thing I got from the other thread is that it is a matter of personal taste. The other thread also ended up comparing apples to oranges and I can't honestly say that I know someone with a powerboat that uses the same yanmar as I. Wish I did to compare notes and experiences. The idea to build a highly efficient powercat is a good one. Anything that gets you out on the water and having fun can't be knocked.

[witzgall]

This made me think of that sailboata designed to fit into a container. That might make a nice powerboat....

Originally Posted by xort

Try finding a mid sized off-the-shelf power boat with a configuration like Dashew's Un-sailboat. Don't forget that he gets a big benifit from the very long waterline and very narrow (relatively) beam. That sort of power boat doesn't exist in the under 45' range.
The BEST fuel consumption figure I've seen in mid-sized power is 4 mpg. Most are 2 to 3 mpg. Comparable sail will get 6 to 8. That's double to triple the economy for AVAILABLE mid size craft.
Build your own is a totally different set of rules.

[44'cruisingcat]

Originally Posted by xort

Try finding a mid sized off-the-shelf power boat with a configuration like Dashew's Un-sailboat. Don't forget that he gets a big benifit from the very long waterline and very narrow (relatively) beam. That sort of power boat doesn't exist in the under 45' range.
The BEST fuel consumption figure I've seen in mid-sized power is 4 mpg. Most are 2 to 3 mpg. Comparable sail will get 6 to 8. That's double to triple the economy for AVAILABLE mid size craft.
Build your own is a totally different set of rules.

Seeratlas says he gets 8 nmpg from a 40 foot heavy displacement steel yacht under motor, at 8-9 knots. This boat has a sailing rig and the appropriate ballast fitted, so it's safe to assume that if you built a similar boat, with similar power, but didn't fit either rig or ballast, these figures would improve. Based on that I would say Dave's targets will be easily met and/or exceeded.

[Seeratlas]

Originally Posted by 44'cruisingcat

Seeratlas says he gets 8 nmpg from a 40 foot heavy displacement steel yacht under motor, at 8-9 knots. This boat has a sailing rig and the appropriate ballast fitted, so it's safe to assume that if you built a similar boat, with similar power, but didn't fit either rig or ballast, these figures would improve. Based on that I would say Dave's targets will be easily met and/or exceeded.

Not to split hairs, but i said cruising at 7.5 to 8 knots I burn just a smidgen under or right at 1 US gallon, with no sail standing. I can do 9 knots without problem, but the *sweet spot* appears to be the northside of 7.5 knots. Of course, Motorsailing with the rig up in light air conditions (meaning enough air to sail, but not at that speed without motor assist) I can do better. oh, and the boat is 44', 13ft beam 5'8" draft.

seer

[44'cruisingcat]

Apologies for my slight inaccuracies. The point is, you say you are acheiving nearly 2nm per litre, (1 US gallon = 3.78 litres) with a heavy steel monohull, including rig and ballast. It's fair to say that without the rig and ballast your boat could do even better.

Catamado is only aiming at acheiving 1 nm/l, with a far lighter boat, with a longer waterline, around 13:1 length/beam ratio, and no rig or ballast. I would say your boat is proof that his targets are easily attainable.

[Seeratlas]

Originally Posted by 44'cruisingcat

Apologies for my slight inaccuracies. The point is, you say you are acheiving nearly 2nm per litre, (1 US gallon = 3.78 litres) with a heavy steel monohull, including rig and ballast. It's fair to say that without the rig and ballast your boat could do even better.

Catamado is only aiming at acheiving 1 nm/l, with a far lighter boat, with a longer waterline, around 13:1 length/beam ratio, and no rig or ballast. I would say your boat is proof that his targets are easily attainable.

I would likely agree that he may be able to reach his design goals. There are lots of parameters. My boat seems to have an excellent match between motor/hull/and prop. Some are not so fortunate.

seer

[cat man do]

I think if you feel you have bettered one litre/NM and achieved 2 with a boat that has a 3.3:1 finesse ratio, I will $hit it in with a 12.5:1 finesse ratio.

The projected speed and efficiency that I have stated are from the prop guys that have a reputation of being fairly conservative in the industry, so it will more than likely do better, as the vast majority of their projections do.(worked out on numbers provided by client)

Posted by Seeratlas
My boat seems to have an excellent match between motor/hull/and prop

They and others have also commented on the sliperyness of the hull which is a very efficient performance sail hull modified, compared to a straight power type hull that relies more on HP to break any speed contraints.

I also let them choose props and placement and their choice of engine was mine as well, and then the positioning of the engine was dictated by efficiency, not accomadation., therefore getting about a 3degree shaft angle.

Rudders were also built with efficiency in mind and are actually a wing tip shaped foil like a spitfire, not just a flat metal blade like most powerboats.

Posted by Seeratlas
I would likely agree that he may be able to reach his design goals.

I feel I will better my design goals as I have used tried and proven methods, Long waterline length,high finesse ratio, low weight = low power requirement for given speed and fuel consumption.

Posted by Seeratlas
cruising at 7.5 to 8 knots I burn just a smidgen under or right at 1 US gallon, with no sail standing. I can do 9 knots without problem, but the *sweet spot* appears to be the northside of 7.5 knots. the boat is 44', 13ft beam 5'8" draft.

But I am happy to state conservative numbers for my vessel at the moment.

Dave

[Seeratlas]

LOL, Cat, you need to relax a bit. Even when you hit your fuel target,,, you will still use fuel for every nautical mile you ever go, for as long as you go. Between my sails, and the parallel diesel/electric drive/solar cells, windgen, and 8kw genset, my overall *avg* fuel use will stomp hell out of whatever you ultimately manage.

Over a ten year span of constant cruising between Nova Scotia and Brazil, the boat required filling the tanks about twice a year....My new electrics will further reduce these numbers substantially. I seriously doubt the price of marine diesel is going down anytime soon. More than likely, it is going on up, substantially.

Even amortizing the rig, (each individual panel sail lastly vastly longer than normal sails, while being easily made on the boat, in transit, ) my sail replacement cost over time is drastically less than you have allowed in your computations. As I have no standing rigging, My sail related costs are pretty much limited to a bolt of sailcloth, thread, a few fittings, and some new line every now and then.

In any event, You will have a fun boat well suited for your application. For doing the roundyround, I'm happy with the Pearl. Sooner or later I'll probably see you out there. Have had a fondness for the land of Oz since the mil blokes I was with in Darwin offered me my first 'stubbie' (tho I don't remember much of what happened after...lol

seer

seer

[cat man do]

Have fun with your choice of boats seeratlas, I could never be happy with that style of boat as it would be totally unsuitable for the type of areas I will cruise and times that I wll be there.

Big offshore reef cruising needs calm weather and motors, though your sails will be nice (though expensive) shade structures

Enjoy

PS: I still would be interested as to how your vessel under motor gets better fuel efficiency than almost any other vessel on the planet.

Dave

[Celestialsailor]

Didn't we just beat this topic to death in another thread?