Fred:

I would guess that 1 hp per thousand pounds of boat weight would move you at
sqrt(LWL). Your 26' has about 24' of water line length, so the speed would
be 4.9 kts = 5.7 mph. I would guess that your 26' would weigh about 6-8,000
lbs loaded for cruising, so 6-8 hp. This would be a reasonable cruising
power from a 9.9 hp outboard.

MPG is a little tougher. I would guess that a small 4 cycle outboard is
going to put out about 10 hp per gallon per hour, so figure about 3/4 gph or
7-8 mpg.

I think I would look for a large frame (Most o/bs use the same block for 9.9
and 15 hp. I would look for one with the most displacement and not just a
carb/cam increase from a 10 hp model.) 15 hp engine and run it about 2/3 of
WOT. You might get an extra knot or so.

Drawbacks- noise.

David
----- Original Message -----
From: "Frederick Flinn" fjflinn@sbcglobal.net
To: trawlers-and-trawlering@lists.samurai.com
Sent: Saturday, January 05, 2008 12:37 PM
Subject: T&T: boat speed with outboard

Fred,

Most all swim platforms are designed to hold the weight of one or two
people, and are not designed to take the structural loads involved in the
thrust of a motor propelling the boat. Their structure as well as their
mounting to the hull in most cases are just not designed for that service.

If you are talking about that setup for an emergency propulsion system, that
would be one thing. On the other hand, if you are looking to that as a way
to cruise for a substantial distance in multiple weather conditions, I would
seriously caution you to look for a more seaworthy set up.

Kevin

Fred,

If you do decide to go with a small outboard there are several sizes to
choose from that might work, and there are strong enough transom mounts
to support up to 25hp.  Here's an example:

http://www.garelick.com/product.php?pnumber=71095

We had a 22' C-Dory with a 9.9hp outboard kicker.  The C-Dory was light
(3,000 lb loaded) and very shallow draft - almost no deadrise.  The 9.9
would push it at 6 knots.

Now we have a moderately deep-v 11,000 pound 26-footer with 9.9 Yamaha
four-stroke high-thrust kicker.  The kicker maxes out at 4 knots.  I
don't have an accurate measure of its fuel economy, but I don't think
it's as much as 7-8 mpg.  My estimate is 3-4 mpg.  We drag the stern
drive through the water to some degree, which isn't terribly efficient,
even when it's up as far as we can get it.

Have you considered a 26 or 27-footer with diesel?  Ours has a 260hp
Volvo KAD44 duo-prop diesel, and gets 3-4 nmpg at 6.5 knots, even though
it can cruise at 18 knots.  We travel mostly at 6.5 knots, for months at
a time, on the coast of BC and SE Alaska.

I don't know much about express cruisers, but there are cabin boats that
might do well for you on cruising comfort and economy.  Here's one
example that comes with a moderate size diesel - more economical than
ours, I'd guess.

http://www.rosboroughboats.com/sedan_cruiser.html

Here's a used one with diesel:

http://adcache.boattraderonline.com/6/4/4/91420744.htm

SeaSport boats out of Washington also makes 26-27 footers with diesel.
They're more like our boat.  SeaSport's 27 Navigator also comes with a
flying bridge.  Here's a non-flybridge example:

http://adcache.boattraderonline.com/6/5/9/90357659.htm

Richard Cook
New Moon (Bounty 257)

Frederick Flinn wrote:

I am not an expert but I remember someone in our club doing this. He
had two smallish outboards in a ring on the stern in a fairly heavy
boat. He found that he had lost of trouble controlling the boat
because the small high reving props did not have enough torque to push
the boat in any serious wind or sea conditions.

Is HP alone a means of computing the best power for a vessel.

Much of the northern loop is in canals but even in those canals much
is in open areas where seas and winds can be a consideration. I
believe one recent looper in his summary said the worst day on the
trip was in Lake Simcoe on the Trent.

On Jan 5, 2008 3:37 PM, Frederick Flinn fjflinn@sbcglobal.net wrote:

--
Greg and Susan Han
Allegria -- Krogen Whaleback #16