query about adding a fixed trim plate

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richg99 - 22 Sep 2003 02:21 GMT

I have a 14 ft. Carolina Skiff that does everything right...except...get up
"on to plane "quickly.

I recently traded in her older 25 hp Johnson, equipped with a Stainless
steel prop, for a newer 25 hp Mercury. The Mercury came with, obviously, a
different plain aluminum prop. I have not discarded the idea that the prop
may be the answer to my puzzle...

Previously, with the older Johnson, the boat would plane out in a very short
time. I run her in West Galveston (TX)bay flats, and that means running,
most of the time, in 9 inches or so of water. With the older engine, I had
NO problem getting her up and running in very shallow water.

The new motor (25 hp mercury) doesn't get her up as fast last as the older
engine. It is entirely possible that the pitch of the "standard" prop is not
sufficient to give me a "hole shot" that the older one did.

I will probably bring the new prop in for adjustment.

I did, however, have the idea that I could simply build a few L shaped hull
extensions that would act as permanent trim tabs, and that might solve the
"getting up" problem permanently, and even add a little speed. The
extensions might eliminate re-working the prop.

Any thoughts or comments from this group would be appreciated.

RichG

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Stephen Baker - 22 Sep 2003 02:32 GMT

Richg99 says:

>I have a 14 ft. Carolina Skiff that does everything right...except...get up
>"on to plane "quickly.

<snip-de-dip>

>Any thoughts or comments from this group would be appreciated.

First of all, get the prop checked, and if possible compare pitch/rpm to the
old one.
Don't even think of putting holes in the hull until you have tried every other
avenue. A hole is just a sinking waiting to happen (although in 9" of water
you probably aren't worreid about much more than getting your shoes wet!)

Steve
Stephen C. Baker - Yacht Designer
http://members.aol.com/SailDesign/private/scbweb/home.htm

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Brian Whatcott - 22 Sep 2003 03:56 GMT

>I have a 14 ft. Carolina Skiff that does everything right...except...get up
>"on to plane "quickly.
[quoted text clipped - 7 lines]
>sufficient to give me a "hole shot" that the older one did.///
>RichG

Let's raise the issue up from a level of "entirely possible"
by reading both the old and new prop data, and sharing the numbers
with us.

It is usually cast into the hub area of the prop.
If no numbers show up, The diameter is easy to measure,
the pitch not so easy, but reading the angle of a blade at the same
point on both props would give a clue, even if no numbers are to be
found.

Either too high or too low a pitch can make for slow lift onto the
plane.

Brian Whatcott Altus OK

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Bill Sheffield - 25 Sep 2003 21:03 GMT

Compare your old prop and your new one first........
Some of the Carolina Skiff boats have a "hook" already built into the hull
to help them plane better with small motors. Fixed tabs at the angle needed
to plane quickly will force the bow down too much at speed, resulting in
plowing and slower top speed. Try one of the hydrofoils mounted on the
cavitation plate, or try some of the "automatic" tabs that are available.

Bill Sheffield

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Boat Forum / Building / September 2003

query about adding a fixed trim plate