Re: Hawaiian trade wind P14/15 HP race & hull speed

Gregory S. DeLozier (delozier@aristar.com)
Fri, 6 Nov 1998 10:35:17 -0500


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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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Hi,

GSTahoe writes...

>Rich--
>
>With a P-15 in 20 knot winds with attendant chop if you where to race three
>boats, one with a Honda 2, One with a Tohatsu 3.5 and one with a Honda 5
from
>island to island, I'm afraid it would be a dead heat. All three would push
>your P-15 at hull speed.

With all due respect, I must disagree. The reason the speed of a boat
is limited by hull speed is that at speeds above hull speed, the boat
must climb its own bow wave. As it turns out, planing boats do this
all the time; for instance, a Sunfish or Capri sailboat can generate
enough power _under sail_ to climb its bow wave and plane...

However, that resistance (climbing the bow wave) isn't the only thing
that limits a boat's speed. If the headwind presents so much resistance
that the bow wave climb isn't reached because the motor can't go that fast,
then the hull speed isn't the issue. The issue is: do I have enough
power to reach the hull speed to begin with in the face of this headwind/
chop/etc?

I'd agree: in a boat that can't plane (and it isn't clear that the P15 is
such a boat, but for now we'll say that it is) then two motors that
will reach hull speed will finish at basically equal times. However,
I can easily imagine conditions where 2hp wouldn't push a big
bluff bow like the P15 has at hull speed at all.

Consequently, I suspect that while perhaps the 5hp and 3.5 hp
engines might be equivalent, the 2hp model might not keep up
so well.

As a final comment, if it takes, say, 3hp to reach hull speed
under a given condition, then a 5 hp engine can put out 3 hp
all day long a lot easier than a 3.5 hp engine run nearly
flat out. So if you think you're going to need to power the
boat for long distances, a motor that's a little overrated won't
hurt, providing the weight isn't an excessive issue.

Just comments from a guy who's been there. :-)

To keep things in perspective, the engine for the E29 I'm
restoring is going to set me back about $6000. And that
doesn't include the propellor!

Best wishes, and fair winds...

-greg