Upgrade Evenrude 9.9 hp outboard

Upgrade Evenrude 9.9 hp outboard

Post by Ed We » Thu, 04 Jan 1996 04:00:00


I have a 9.9 hp Evenrude outboard that is an aux. for my 28' Lancer sail
boat.  The boat is 3/4 keel with 6,000 lbs. displacement. I have be told
that this engene can but upgrade to 15 hp. by simple modification to the
carberator. Has anyone had experience with this proceedure?

Second question, will the increase hp give me any more speed?  I don't
have any way of measuring speed on the boat other that a hand held GPS,
which indicates I get 5 to 6 knots under power.

Thanks.

Ed Welp
Seaclusion
Chesapeake, VA

 
 
 

Upgrade Evenrude 9.9 hp outboard

Post by Paul D Shepa » Fri, 05 Jan 1996 04:00:00


Quote:

>I have a 9.9 hp Evenrude outboard that is an aux. for my 28' Lancer sail
>boat.  The boat is 3/4 keel with 6,000 lbs. displacement. I have be told
>that this engene can but upgrade to 15 hp. by simple modification to the
>carberator. Has anyone had experience with this proceedure?

>Second question, will the increase hp give me any more speed?  I don't
>have any way of measuring speed on the boat other that a hand held GPS,
>which indicates I get 5 to 6 knots under power.

>Thanks.

>Ed Welp
>Seaclusion
>Chesapeake, VA

Sounds like that you have already achieved hull speed. A
bigger motor will not help you go any faster if that
is the case. It will help you if you are pushing
against a current, towing something heavy. I forget the hull
speed formula, something like 1.4 or 1.14 times the square
root of your waterline



 
 
 

Upgrade Evenrude 9.9 hp outboard

Post by Wayne Beardsl » Sat, 06 Jan 1996 04:00:00

Quote:
>Sounds like that you have already achieved hull speed. A
>bigger motor will not help you go any faster if that
>is the case. It will help you if you are pushing

                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Quote:
>against a current, towing something heavy. I forget the hull

  ^^^^^^^^^^^^^^^^^^

Quote:
>speed formula, something like 1.4 or 1.14 times the square
>root of your waterline


Nope, sorry but a bigger motor will most definitely not help you push
against a current if you are already going at hull speed.  Hull speed
is based on speed thru the water, not speed over ground.  The correct
multiplier is about 1.3 times waterline length squared, e.g., hull
speed for a boat with a 25 foot waterline is about 6.5 knots.

 
 
 

Upgrade Evenrude 9.9 hp outboard

Post by Michael Du » Sun, 07 Jan 1996 04:00:00

Hull speed is a theoretical number determined by a formula, as
noted in other follow-ups in this thread.  There are hulls which
are obviously displacement, others obviously planing, and a full
range in between, it's not always a black and white.  The
multiplier can be anything from about 1.34 to 1.50, times the
sq. rt. of the waterline.

Other factors also influence max speed of the boat - wetted
area, wetted shape, etc.

Sounds like 5-6 kts is about the right max speed for your boat,
considering the specs for the Lancer.

Does this help to muddy the waters a little more ? !

Michael Dunn, Shdiac, NB, Canada

Quote:

>I have a 9.9 hp Evenrude outboard that is an aux. for my 28' Lancer sail
>boat.  The boat is 3/4 keel with 6,000 lbs. displacement. I have be told
>that this engene can but upgrade to 15 hp. by simple modification to the
>carberator. Has anyone had experience with this proceedure?

 
 
 

Upgrade Evenrude 9.9 hp outboard

Post by Steve Ott » Sun, 07 Jan 1996 04:00:00


Quote:

>I have a 9.9 hp Evenrude outboard that is an aux. for my 28' Lancer
sail
>boat.  The boat is 3/4 keel with 6,000 lbs. displacement. I have be
told
>that this engene can but upgrade to 15 hp. by simple modification to
the
>carberator. Has anyone had experience with this proceedure?

>Second question, will the increase hp give me any more speed?  

Your boat sounds like it has a displacement hull rather than a planing
hull.  Therefore, it has a definite maximum speed based on a formula
(which I've forgotten) which takes into account your hull length.
Probably increasing the hp of your engine won't get you much of an
increase in hull speed, if any.  Your hull will just try to push more
water out of its way, with the ultimate effect of burying your bow in a
big wave ahead of it.  Spend your money on something else nice for your
boat instead.
 
 
 

Upgrade Evenrude 9.9 hp outboard

Post by Paul D Shepa » Tue, 09 Jan 1996 04:00:00


Quote:

>>Sounds like that you have already achieved hull speed. A
>>bigger motor will not help you go any faster if that
>>is the case. It will help you if you are pushing
>                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>against a current, towing something heavy. I forget the hull
>  ^^^^^^^^^^^^^^^^^^
>>speed formula, something like 1.4 or 1.14 times the square
>>root of your waterline

>>Paul D Shepard

>Nope, sorry but a bigger motor will most definitely not help you push
>against a current if you are already going at hull speed.  Hull speed
>is based on speed thru the water, not speed over ground.  The correct
>multiplier is about 1.3 times waterline length squared, e.g., hull
>speed for a boat with a 25 foot waterline is about 6.5 knots.

Yes, if you already going hull speed it will not help, That's  what
I said. If you are going against the current and not achieving hull speed
then it will help you. I thought that was clear, sorry if I didn't
make my point more clear.