Small Full Displacement Cruisers

[djmarchand]

Samson:

There are several types of hulls:

1. Round bottom
2. Hard chine- flat deadrise (angle of the hull looking at the stern)
3. Hard chine- deep keel, deep deadrise, so called deep v bottom
4. Soft chine or rounded chine

And some of these have no keel, a stubby keel or a deepish keel. #2 through 4 can be pushed beyond displacement speed with enough horsepower so are considered semi displacement hulls.

A "true downeaster" as produced by the New England custom boatbuilders has a deep, full keel, a flatish deadrise and a soft chine. It isn't particularly fuel efficient but it is very seakindly.

[bathharbor]

How about a Nimble , made as a motorsailer or powerboat , another is the Cape Dory 28 Power Boat

[Todd D]

I can't comment on current small displacement cruisers. However, there were a lot built back in the 20s and 30s. I own a 1936 vintage 32' displacement cruiser that I am in the process of repowering. The boat has a displacement of approximately 10,000 lbs. With its 32' LWL the nominal hull speed is about 7.6 knots. As part of the repowering exercise I did a fairly complete analysis of the power needs for a small displacement cruiser. That analysis is summarized at:

http://www.todddunnmicroyachts.com/tortuga/repower.html

A displacement hull running at speed to length ratios up to about 1.6-1.7 doesn't need all that much power. With the exception of the Willard 30 and the small Albin cruisers, almost none of the newer boats are powered for pure displacement cruising.

Just my thoughts on the subject.

[samson]

Originally Posted by samson

reading this from the nordic 26 info.

"Though her 115 hp (86 kw) Cummins diesel burns less than one gph at six knots or two gph at eight knots,"

how is that? i have been doing all sorts of numbers and things and im seeing yanmars 20 and 30hp barely burn less then 1gph or around .7gph to put a displacement hulled boat under 30 ft to hull speed. that is a HUGE difference from 30hp to 115hp.

John

any one know why this is
thanks
John

[markpierce]

It has more to do with how much horsepower one is actually producing rather than the amount capable of producing.

[David_Old_Jersey]

Originally Posted by Todd D

That analysis is summarized at:

Repowering Tortuga - Choosing a new Engine

That's an awesome reference point for anyone thinking of a re-power

I dunno how good it all is (some ) of the technical stuff is way beyond me, but seems ballpark to me.

[GordMay]

Greetings and welcome aboard the CF, Todd D.
Thanks for sharing your interesting & informative analysis.

[NewMoon]

FWIW - there was an earlier post which said that a Nordic Tug 32 would get only 2 nmpg at 7 knots. My friends cruise the Inside Passage in one, and it gets about 4 nmpg at 7 knots. With its 210 hp diesel it can do 14 knots or more, but it's quite happy and reasonably efficient at 7. Push it up to 8 or 9 knots and fuel mileage declines significantly. Keep it nearer hull speed and it works quite well.

[u4ea32]

Originally Posted by NewMoon

FWIW - there was an earlier post which said that a Nordic Tug 32 would get only 2 nmpg at 7 knots. My friends cruise the Inside Passage in one, and it gets about 4 nmpg at 7 knots. With its 210 hp diesel it can do 14 knots or more, but it's quite happy and reasonably efficient at 7. Push it up to 8 or 9 knots and fuel mileage declines significantly. Keep it nearer hull speed and it works quite well.

Your friend may be correct: I think the 2.1 nmpg we saw was at 8 knots, not 7. I stand corrected.

[C.E. Grundler]

I wouldn't buy anything but full displacement single screw. The less your fuel budget, the more you can cruise. My 1977 32' Cheoy Lee trawler with a 80 hp 4 cylinder Lehman cruises at a comfortable 7 knots on 1.5 gallon per hour, and is very capable in ugly conditions. I know this is slightly over your 30' limit, though there were a few 28' models built.

[HopCar]

In that size range there are very few full displacement boats. If you are set on full displacement, there is no shortage of plans for this type of pocket cruiser. Build one or have one built. If you don't mind going a little faster, take a look at the Ellis line of "real Down East boats". I have a twenty year old Ellis 28 that I love. When I had it built I thought I would be doing a lot of scuba diving so she has a big cockpit and minimum living quarters. If I was doing it today, I'd do the opposite.
Another small cruiser that I've been drooling all over at boat shows is the Camano 30. Looks like a very comfortable boat for two with a huge flying bridge. I'm in Florida so being able to run the boat from topside is important.

[motion30]

I must admit I not sure I understand the difference between the two I have a trawler and it is semi displacment what is the difference?

[Adelie]

Originally Posted by Todd D

I can't comment on current small displacement cruisers. However, there were a lot built back in the 20s and 30s. I own a 1936 vintage 32' displacement cruiser that I am in the process of repowering. The boat has a displacement of approximately 10,000 lbs. With its 32' LWL the nominal hull speed is about 7.6 knots. As part of the repowering exercise I did a fairly complete analysis of the power needs for a small displacement cruiser. That analysis is summarized at:

Repowering Tortuga - Choosing a new Engine

A displacement hull running at speed to length ratios up to about 1.6-1.7 doesn't need all that much power. With the exception of the Willard 30 and the small Albin cruisers, almost none of the newer boats are powered for pure displacement cruising.

Just my thoughts on the subject.

After going thru your summary and analysis I noted at the end that while the engine you chose was $200 more than the cheapest, given the better fuel economy at 6.5kt, at $4/gal you will break even on that $200 difference after 1000hr running. So unless you get rid of the boat in the next 5yr (ignoring inflation and assuming 200hr/yr running time) you will be money ahead)

[alohaboat]

The Willard 30, a true full displacement trawler wth ballasted keel, with a stock 30hp Yanmar engine, burns .6 gph at around 5.5 knots. That is around 9 nmpg. The W30 carries 150 gallons of fuel aboard for an "all out" range around 1400 nm.

Nordic Tugs are semi-displacement hulls with somewhat greater interior space than the Willard 30. But fuel efficency is the big difference between displacement and semi-displacement hulls.

My Willard 40 with a 120hp John Deere diesel burns under 1.5 gph at 7.5 knots for a comparable 5 nmpg. With 700 gallons of fuel in the tanks I have an ultimate range of around 3500 nm.

Patrick
aboard ALOHA
La Paz, MX

[Potuguese]

....I know it is too late but You could see this!
::: FLAB :::
It has a Yanmar diesel 28 HP and the first hull has already 3500 miles in open waters and ZERO problems...Check it out!