518Re: [AtkinBoats] Easily driven boats
- Jan 17, 2005Leo--
When slow turning motors were very heavy and conventionally planked (carvel or lapstrake) were developed to float them, boats were kept in the water, and trailering was not a consideration.
If you want a boat that can live on a trailer, the first consideration is the type of tow vehicle you are willing to support. The big trucks and truck based sport utes can tow a pretty big boat; most cars can only tow around 1000 to 1500 and at the upper ends of this limit, gas consumption will decline significantly.
Then you need to consider how well a given type of construction will hold up to being dry sailed and bounced around on a trailer. Carvel won't take it. Boats which rely on lots of mechanical fastenings tend to get real loose after a couple of hundred miles on rough roads. Probably plywood or fiberglass over strip planking are your best bets.
I have looked for "big ol slow turning engines", and I haven't found any yet--seems I'm about 10 to 15 years too late. The closest thing I've found is a variety of kits for steam engines. They look like a lot of fun, but I don't have the skills or tools to build one, nor the committment to run one.
As far as getting all the amenities you are looking for in an easy to trailer boat, I just don't think it is possible. If you figure it out, let me know!
----- Original Message -----
Sent: Monday, January 17, 2005 3:35 PM
Subject: [AtkinBoats] Easily driven boats
Back when internal combustion engines were first becoming available -
whether gas or diesel - these engines were massive chunks of cast
iron and had very low HP to weight ratios. Maybe on the order of 1HP
per 100 pounds. Today's engines might have 10-20 HP output per 100
pounds of weight. Refer back to the comments about Rescue Minor and
how the bow acts without the motor weight that Atkin specified for an
So back when Atkin was designing, motors were very underpowered and
the hull really needed to be "slippery" to fully take advantage of
the low power that was available in those days from IC engines. And
yes, I know I'm sorta downplaying, for now, the effect that torque
has on turning a large propeller slowly.
Based on my reading, early displacement power boat hulls evolved from
sailboat hulls that were "sorta" efficient. Obviously the science of
designing efficient displacement power boat hulls progressed rapidly -
as NA's learned what worked best and what was less desirable.
It seems to me that as engines become both more powerful and the
power to weight ratio improved, that the hull shapes started moving
away from what slipped through the water easiest and began evolving
into the "fat-ish" hulls of trawlers and cargo boats and that
evolution has progressed into the modern plastic floating apartments
that grace (or is that disgrace?) trade magazines and marina's the
Having recently read a history of the Whitehall Rowing boat, I began
to wonder why this hull form, with its fine entry, generous mid-
section and wineglass stern wasn't expanded upon for inboard power.
What's the drawback from scaling this general design up to make it a
30-40 footer? Perhaps direct 1:1 scaling isn't practical, but why
couldn't one incorporate the fine entry, general midships section and
the fine stern sections into a power boat hull? To my very untrained
eye, it appears that Atkin did use some of these three design
principles in several of his designs.
IIRC, from Gerr's books and others, a large diameter, aggressively
pitched slow turning propeller is more efficient for moving a
displacement hull than a smaller less pitched propeller turning at
higher speeds. Or is my memory getting as gray as my hair?
It seems to be a difficult task in today's world to find folks that
agree with this philosophy. Almost all modern (inboard diesel) boat
propulsion systems rely on high speed engines - many with
turbochargers - to turn a smaller wheel. Gear ratio's in the 2:1 -
2.5:1 are common. This translates into prop RPM's from the low range
of 750 RPM to a high of 1800 RPM when the 2:1 geared engine is wound
to 3600 RPM.
Yet just a few decades ago we had engines that idled at 300-400 RPM
(or less) and had an operating RPM range from 700 to 1200. These
engines ran for literally tens of thousands of hours nearly trouble
free. Nowadays we often hear of inboard diesels needing replacement
in as little as 2000 operating hours. Throwaway power. Yuck!
I believe that we can generally agree that 1) how/where you want to
go with a boat, 2) how long you want to stay aboard and 3) how
much `camping' you're willing to tolerate determines what type, size
and amenities we'll need. And finally, 4) aesthetics. How a boat
looks to our eye is vital. And as each of us has different needs and
tastes, I believe all 4 of these considerations are classic cases
where Your Mileage May Vary. ;-)
Addressing #1. My wife is a teacher and a decade younger - I want to
be able to put the boat on a trailer and go for her summer vacation
to Alaska via the inside passage this summer, The Erie Canal next -
Maine and Nova Scotia another - Trent-Severn waterway another. When
we're both retired then on to the Bahamas for the winter and back to
Alaska for an extended trip. Maybe put it aboard a freighter and
ship it to France for a couple of years living on the European canal
Addressing #2. At first we're only talking about 10-12 weeks at a
stretch. Later it could be full time for a few years - or at least 8-
9 months out of 12.
Addressing #3. At first - we can tolerate a bit more `roughing it'
for a few weeks, but some of the things that we will not do without -
(not an all inclusive list) 1) space to get away from each other when
need to. 2) a great galley with room enough to prepare a full meal
without contortions of the body or with the pots and pans. 3) full
length and width berth(s) with comfy mattresses. 4) a separate full
sized shower - no sopping TP! 5) an all weather pilot station -
either fully enclosed or enclosable with canvas.
Addressing #4. I just plain like boats that look like a classic
boat. None of this plastic fantastic modern European shapes for me.
Give me the lines of an Elco or a Lake Union Dream Boat or a double
ended Salmon Troller or the shape of a Whitehall. Give me a nice
sheer and a plumb bow. How about bronze ports - either oval or
round - and a rearward sloping windshield instead of that forward
sloping monstrosity, regardless of how practical it is. Bottom
line? Spare me the angular constructs that adorn so many marina's
and boat shows.
Finally, I think we can all agree that petroleum products - oil, gas,
natural gas and diesel fuel - are just going to get more and more
expensive. The days of a buck a gallon diesel are probably long
gone. So this means that to have a boat that I can afford to
operate, it must be very efficient. I'd consider 7-10 statute MPG
the minimum - this should equate to less than 1 gallon per hour of
running, in other words, 6-8 knots cruising speed at less than 1
GPH. Better than that is just that, better. I think that this is
achievable in a 35'-ish boat if we don't load it down with a ton of
canned goods. Something less than 20,000 pounds - 15,0000 better
yet - fully ready to cruise would be the goal. My preliminary
investigations and calculations indicate that given the right hull
design and using modern epoxy/ply building methods this appears to be
an achievable goal.
Finally, utilize a big ol' slow turning engine with either a VPP or a
big-ish wheel and set it up to cruise at a V/L of about 1 to 1.15 at
the most efficient fuel consumption RPM for the engine - probably
less than 1500 RPM - and one should have a boat that one could afford
to build and run without breaking the 401k and would be worthy of
being called a Retirement Cruiser.
Addressing Manfred's comments about River Belle - This would be a
perfect boat for cruising the ICW and the various canals, waterways
and rivers. But would this design be suitable for an Alaska trip or
a trip to the Bahamas or a summer on the Great Lakes or the coast of
Maine and Nova Scotia and Newfoundland? Perhaps not. So I still
think to go to all the various places that I'd like to visit before I
die, I need a boat with some sort of keel and the ability to take
some rough weather should the unfortunate happen.
Any other suggestions?
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