economical coastal cruiser

Not the case with modern concepts like the LCS, Earthrace and one or two of similar ilk. These boats are designed to wave pierce so do not ride over the waves but go through them.

Similar to higher volume and much heavier boats they are very wet so are operated from enclosed cabins with streamline windows as they will be submerged in certain sea conditions.

Rick W

 

As I would expect your stabilized tri-err ah monohull to be. A very wet and rough ride.

What you are suggesting to me is that parting a wave exerts little force on a hull?

 

The true wave piercing designs have very slender and low height entries relative to the rest of the hull. The low volume in the front reduces the pitching. The hull and deck must be designed to achieve some dynamic lift so they do not dive.

I am not suggesting the hull I proposed earlier is intended to be wave piercing but with lower internal volume and more streamline shape it could be.

The lowest drag hull for any displacement is a submarine. Their entire hull parts the water. Water is not immovable.

Rick W

 

I have towed a C-Dory 25 from coast to coast, twice. The boat and trailer weighed 8700 lbs (1500 for trailer alone). I believe a 1/2 ton pickup might be a little small for that kind of load. I use a Dodge 2500 with diesel, 6 spd manual, and 4 wheel drive. We never had a problem with launching and retrieving, however we did use the 4 WD several times. On a trip from Missouri to Monterey, CA I managed to get 11mpg, but only with constant attention to the fuel use computer.
When no water was near, we overnighted in Rest Areas, Truck Stops, and Walmarts.
No better way to travel, and hope to get back to that life soon. Anyone want to buy a 52' fuel guzzler?

 

It is a bit optimistic.

The core engine of the vetus 32 hp is the mitshubishi S3L2. It is also used on genset, where they do publish data on fuel burn:

At 3000 rpm:
www.celec.se/custom/file.php?filename=T20HK.pdf
Stand by power = 20,9 Kw. Prime power = 20.9/1.1 = 19 Kw.

Fuel burn 19Kw @3000 rpm = 6,7 liters. Per Kw 0,35 l/Kw.
Fuel burn 75% @3000 rpm = 5,5 liters Per Kw 0,385 l/Kw.


At 1800 rpm:
http://www.dieselgeneratorsmiami.co...DIESEL GENERATOR DATASHEET T11U (ENGLISH).PDF

Stand by power = 13.86 Kw. Prime power = 13.86/1.1 = 12.6 Kw.

Fuel burn 50% @1800 rpm = 2,5 liters Per Kw 0,396 l/Kw.

And that is without gearbox losses.

A correct figure for low power diesel engines would be:
0,4 l/Kw 9.4 Kw per gallon, 12.8 hp during one hour per gallon.


It is still better than outboards, but not that much. You need to compute how it will cost you to save a little fuel.

Another point, the inboard diesel engine will be heavier than the outboard by some 250 lbs . You need to include that in the costing. Either you save that weigh in the building: ie increase significantly construction cost and add that cost to the already more expensive diesel engine, or the fuel burn will have be computed for a heavier weigh for the diesel solution.

 

The boat should not need the 1.5kW for the cooling fan. With seawater cooling the fan would be eliminated.

Rick W

 

What turns the seawaterpump ?
How restricted is an exhaust with water injection for cooling ?

 

It already has a pump with its closed system.

Rick W

 

Land engine have one cooling water pump plus one fan.

Marine engine have one cooling water pump plus one sea water pump plus cooled exhaust.

 

Not the little ones with seawater cooling.

Rick W

 

Is there still such engines ?

Below 10 hp, possible, but not bigger.

Direct seaweter cooled engines are catastrophical from an efficiency point, because seawater cannot be as hot as typical engine coolant. Seawater cooled are 60°C engines, Coolant engines are 82-85°C engines. wich allow a hotter engine, and better efficiency.

 

Some data here on a Yanmar about the right size:
http://www.barrus.co.uk/pdfs/3gm30.pdf

It gives 280gph from about 2200rpm upward. Reduction can be 3.2. 700RPM on the prop is about right.

Rick W

 

Don't know - my experience with little diesels is a long time ago. You would need to check with more recent installations.

For long term use I would not like like direct seawater cooling. Also I think Erik wants heating so it would be a bit silly to reject all the heat from the engine.

I doubt that any pump is going to chew up 1.5kW but that was at 3000rpm. The fan at 1800rpm took 0.4kW and that is probably getting down to what a pump would cost to power.

Rick

 

The big advantage of a diesel with its reduced fuel burn comes when you start considering range. At some point the diesel ends up the lighter option.

I don't have much faith in outboard. I believe they have a useful reliable life of about 1000hrs. Most pleasure boats take years to get this many hours up so there are not many that actually get seriously tested. My experience may be out of date with these as well.

My greatest concern with petrol is the higher volatility. I do not like it in boats. Would be interesting to compare boat losses to fire between the different fuels. Maybe someone has the data.

Rick W

 

You do not read correctly the curve.

The 280gr/KW at 2200 rpm is for full load engine. The Vetus engine was given at best (near full load, near full torque ) at 286 gr/KW, yet real figures are worst.


If you take the current engine (3YM30), http://www.yanmarmarine.com/index.cfm/go/Sailboat-engines/ you will see at 3000 rpm 1,1 gph , and 12 Kw at the prop. 10.9 Kw per gallon, and at 2500 rpm 0,6 gph for 7Kw at the prop 11.6 kW per gallon.

But you have to check the price of engine. Yanmar will be 30% to 50% more expensive than Sole or Vetus diesel. Mitshubishi based diesel are among the cheapest. Nothing come for free.