New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything
other than full down trim.

Why?

What to do?

I saw the post on hydrofoil and porpoising, someone suggested that
removing the hydrofoil on his outdrive could make matters worse. How
about the reverse, install a hydrofoil to improve matters? What's the
downside? I am always skeptical about aftermarket devices like these
because you would think that a manufacturer would ofer them standard
or at least as an option if they meaningfully improved performance
with little downside.

According to the manufacturer, trim up improves speed and turning
performance when on-plane. I have not been able to play around with
this much because of the porpoising situation? Therefore, I pretty
much raise the prop only to avoid obstacles at this time. Am I getting
the point of trimming-up as far as boat performance?

Mitch Gossman

Mitchell Gossman wrote:

New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything
other than full down trim.

Why?

What to do?

I saw the post on hydrofoil and porpoising, someone suggested that
removing the hydrofoil on his outdrive could make matters worse. How
about the reverse, install a hydrofoil to improve matters? What's the
downside? I am always skeptical about aftermarket devices like these
because you would think that a manufacturer would ofer them standard
or at least as an option if they meaningfully improved performance
with little downside.

According to the manufacturer, trim up improves speed and turning
performance when on-plane. I have not been able to play around with
this much because of the porpoising situation? Therefore, I pretty
much raise the prop only to avoid obstacles at this time. Am I getting
the point of trimming-up as far as boat performance?

Mitch Gossman

Mitchell Gossman wrote:

New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything
other than full down trim.

Why?

What to do?

I saw the post on hydrofoil and porpoising, someone suggested that
removing the hydrofoil on his outdrive could make matters worse. How
about the reverse, install a hydrofoil to improve matters? What's the
downside? I am always skeptical about aftermarket devices like these
because you would think that a manufacturer would ofer them standard
or at least as an option if they meaningfully improved performance
with little downside.

According to the manufacturer, trim up improves speed and turning
performance when on-plane. I have not been able to play around with
this much because of the porpoising situation? Therefore, I pretty
much raise the prop only to avoid obstacles at this time. Am I getting
the point of trimming-up as far as boat performance?

Mitch Gossman

Do you happen to have trim tabs on that boat?

I do not, what could they do for me and my modest vessel?

Harry Krause wrote in message ...
Mitchell Gossman wrote:

New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything
other than full down trim.

Why?

What to do?

I saw the post on hydrofoil and porpoising, someone suggested that
removing the hydrofoil on his outdrive could make matters worse. How
about the reverse, install a hydrofoil to improve matters? What's the
downside? I am always skeptical about aftermarket devices like these
because you would think that a manufacturer would ofer them standard
or at least as an option if they meaningfully improved performance
with little downside.

According to the manufacturer, trim up improves speed and turning
performance when on-plane. I have not been able to play around with
this much because of the porpoising situation? Therefore, I pretty
much raise the prop only to avoid obstacles at this time. Am I getting
the point of trimming-up as far as boat performance?

Mitch Gossman

Do you happen to have trim tabs on that boat?

On 4 Jul 2004 09:35:28 -0700, (Mitchell Gossman)
wrote:

I do not, what could they do for me and my modest vessel?


You'd be quite surprised..........I talked my uncle into putting tabs
on his 21' Aquasport, and he thanks me every time we take the boat
out. You can trim the boat independent of the drive, and also trim
from side to side. You can also trim the the boat so it planes at a
slower speed, which is great for running in rough water. Most smaller
I/O's are running 20kts on plane, which is way too fast for some rough
water operation. Finally, you can lower the boat in a chop to take
advantage of the sharp hull entry, while trimming the outdrive
separately for ideal thrust.

Lots of benefits even on smaller boats........

Far as I can tell, someone wrote:
install a hydrofoil to improve matters? What's the
downside? I am always skeptical about aftermarket devices like these
because you would think that a manufacturer would ofer them standard
or at least as an option if they meaningfully improved performance
with little downside.

I thought the same thing for a good while.

I used to ride a motorcycle back in the 80's.
To improve comfort, I bought a "Windjammer" fairing, which was a
windshield with "lowers" to protect the entire body from wind and rain.

http://www.xs11.com/tips/modifications/wjv.jpg

It worked very well. Only Harley (and maybe BMW) offered fairings.
Even the famous Honda Goldwing did not have one available from Honda
until years later. Now virtually ALL touring motorcycles come with
fairings standard.

Windjammer went out of business when motorcycles started making their
own.

I certainly agree with you. The needs of people vary so much so
manufacturers want to provide as standard equipment only the bare
minimum rather than provide gold-plated features that may benefit only
a few. For instance, a modest airplane does not require a fancy
autopilot.

BUT...

A wing-shaped piece on the outdrive that could easily be molded into
the rest of the outdrive or bolted on for a few bucks that can
significantly improve performace and specs to brag about in shiny
brochures? Why not?

Far as I can tell, someone wrote:
install a hydrofoil to improve matters? What's the
downside? I am always skeptical about aftermarket devices like these
because you would think that a manufacturer would ofer them standard
or at least as an option if they meaningfully improved performance
with little downside.

I thought the same thing for a good while.

I used to ride a motorcycle back in the 80's.
To improve comfort, I bought a "Windjammer" fairing, which was a
windshield with "lowers" to protect the entire body from wind and rain.

http://www.xs11.com/tips/modifications/wjv.jpg

It worked very well. Only Harley (and maybe BMW) offered fairings.
Even the famous Honda Goldwing did not have one available from Honda
until years later. Now virtually ALL touring motorcycles come with
fairings standard.

Windjammer went out of business when motorcycles started making their
own.

Hi Mitchell,

Is there any way to get more weight up forward in the boat?

When you have you outdrive or outboard fully down tight to the transom and
your boat still porpoises, I believe it is a weight transfer problem?

Maybe when you have a load in the boat with more people, fuel and gear, it
would be just fine and would take some trim without porpoising?

--
Bill Kiene

Kiene's Fly Shop
Sacramento, CA, USA

Web site: www.kiene.com


"Mitchell Gossman" wrote in message
om...

New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything
other than full down trim.

Why?

What to do?

I saw the post on hydrofoil and porpoising, someone suggested that
removing the hydrofoil on his outdrive could make matters worse. How
about the reverse, install a hydrofoil to improve matters? What's the
downside? I am always skeptical about aftermarket devices like these
because you would think that a manufacturer would ofer them standard
or at least as an option if they meaningfully improved performance
with little downside.

According to the manufacturer, trim up improves speed and turning
performance when on-plane. I have not been able to play around with
this much because of the porpoising situation? Therefore, I pretty
much raise the prop only to avoid obstacles at this time. Am I getting
the point of trimming-up as far as boat performance?

Mitch Gossman

"Mitchell Gossman" wrote in message
om...
New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything
other than full down trim.

Mitchell - first and easiest fix could be to put some weight forward. I
would also recommend that you consider trim tabs - either fully adjustable
tabs or "Smart Tabs" type. You can find a lot of discussions on both types
on www.iboats.com forums - search on those two subjects for a lot of (what I
think is) good info. Good luck and have fun with your new boat.

Cam

1. What prop do you have. This is a heavy boat and it needs a good SS prop
w/ some bow lift in it to help hold the bow up when you start trimming. I
would suggest a good SS 4 blade.
2. Trim angle is all about your speed, weight distribution, and
conditions. As you increase speed - you should be able to trim out. If you
are running wide open and bump the trim and the boat starts porpoising -
there is a problem w/ either the prop or the hull or the weight is all
forward.
3. For trim to work - you need less weight in the bow (not more as
suggested). Move weight to the rear (especially a heavy cooler).
4. The hydrofoil will stop porpoise by pushing the bow down (same as
leaving the trim down). It will not help w/ performance in terms of getting
more boat out of the water which is the purpose of trim.
5. Trim tabs do the same thing bow allowing you to push the bow down more.
Will not solve this problem. The are great for helping to plane and stay on
plane at low speed. The also allow you to adjust side to side lean.

Try a 4 blade SS prop. I think it will solve your problem.

--
Tony
my boats at http://t.thomas.home.mchsi.com

"Mitchell Gossman" wrote in message
om...
New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything
other than full down trim.

Why?

What to do?

I saw the post on hydrofoil and porpoising, someone suggested that
removing the hydrofoil on his outdrive could make matters worse. How
about the reverse, install a hydrofoil to improve matters? What's the
downside? I am always skeptical about aftermarket devices like these
because you would think that a manufacturer would ofer them standard
or at least as an option if they meaningfully improved performance
with little downside.

According to the manufacturer, trim up improves speed and turning
performance when on-plane. I have not been able to play around with
this much because of the porpoising situation? Therefore, I pretty
much raise the prop only to avoid obstacles at this time. Am I getting
the point of trimming-up as far as boat performance?

Mitch Gossman