Small outboard power boost
hkr...@capuantispam.net
>
> Dear all
> I need a little more power from a 1998 Evinrude 4hp outboard, used on an
> 8ft/2.4M aluminium tender/fishing boat, to get the little boat to plane (I
> don't want a bigger motor or boat). Any suggestions on how this might be
> done as inexpensively and easily as possible?
> Many thanks
> Paul
Is your boat capable of planing with that size of engine? Have you seen
one like it planing with a 4 hp engine? I had lots of little boats like
that when I was a kid, and I can't recall that one of them planed with
1.5 to 3 hp engines. But it has been a while...
1. Borrow a tach and at WOT, see what your RPM's are. You might not be
getting full manufacturer specified RPM. If not, experiment with props.
2. How does your engine sit on the transom? Is the lower unit as "high"
as it can be while still drawing in enough water to cool the engine? If
the engine is too low on the transom, the lower unit will create more
drag than it should. I used to cut up yardsticks to stick on top of
transom to raise the engine a little. If you do this, make sure you
clamp the engine on properly and use a safety chain to hold it to the
boat.
3. Shift weight around in the boat.
--
Harry Krause
------------
WindowsError 017: Non existent error. This cannot really be happening!
-- Mike --
On Fri, 7 Jan 2000 06:19:30 +1000, "Paul Webb"
<paul...@powerup.com.au> wrote:
>Dear all
>I need a little more power from a 1998 Evinrude 4hp outboard, used on an
>8ft/2.4M aluminium tender/fishing boat, to get the little boat to plane (I
>don't want a bigger motor or boat). Any suggestions on how this might be
>done as inexpensively and easily as possible?
>Many thanks
>Paul
>
In a small boat/motor package, one of the biggest performance gains
can be accomplished by "skipping desert." ;-)
Check what Harry said in his post and you can add "reduce weight, if
possible" to his number 3, where he mentions shifting weight.
I'm not sure of a doel-fin's available, or what it's actual advantage
would be on that small of a setup, but that might be worth looking
into.
I'm not current on new OMC models/hp/years, etc... but if the block is
the same as the next horsepower up, you might try researching to find
out the actual differences. It's humanly possible that the difference
between a 4HP and a 5 or 6 *could be* the carburetor alone.
If you luck out and that seems to be the case, just make sure other
specs are also the same, like timing, etc... If there are any
doubts, don't do it.
I have yet to get into the high-performance world of super-fast 4 HP
outboards...so that is only a guess. Can't hurt to check.
Mike
Mi...@SeilerMarine.com
Lloyd Sumpter
"hydroplane" with 4hp Briggs&Stratton to plane, but there were, well, a
few design flaws...(and I doubt that that old warhorse B&S was putting
out 4 hp)
Have you tried all the planing "tricks": jumping on the bow, or
"waddling" - turning the boat so that essentially one side planes at a
time.
The bathtubs in the Naniamo Bathtub Race use 7.5hp and plane nicely.
(they're about 5-6ft long). The top contenders use hydraulics to trim
the height of the engine. They also use polished 2-blade props. I drove
one once - they're a ball!
Lloyd Sumpter
"Far Cove" Cat 36 - bigger than a bathtub
hkr...@capuantispam.net wrote:
>
> Paul Webb wrote:
> >
> > Dear all
> > I need a little more power from a 1998 Evinrude 4hp outboard, used on an
> > 8ft/2.4M aluminium tender/fishing boat, to get the little boat to plane (I
> > don't want a bigger motor or boat). Any suggestions on how this might be
> > done as inexpensively and easily as possible?
> > Many thanks
> > Paul
>
Paul Webb
Marcus G Bell
Harry mentioned the weight and distribution thereof. I find that
little kickers like these can plane a light boat with one person
in it if it's a kid driving with a cinder block up front for
balast, or if it's a grownup steering from the middle with a
suitable tiller extension. A 1" PVC pipe sometimes fits the
bill.
-- Mike -- (Mik...@usa.net) wrote:
> I'm not current on new OMC models/hp/years, etc... but if the
> block is the same as the next horsepower up, you might try
> researching to find out the actual differences.
I'll spare you the trouble. The engine in question, a 2 cylinder,
4 HP motor, derives from a design that debuted in 1952 as a 3 HP
eggbeater. It was the second engine designed by Johnson and
Evinrude in collaboration, and it's almost surely the oldest
fundamental powerhead design still in production. At its most
powerful, it was 4.5 HP with a FNR gearshift. The deluxe 4.5 was a
junior version of the 7.5 which later became the 6&8 pair sold
today. As such, it had a larger exhaust tube than the current 4,
and probably other modifications to get that extra 1/2 horse.
Even if you replace the carb, reeds, and other bolt-on stuff from
the 4 with that of the 4.5 (and all the linkages match, which they
probably won't), you still have the more restrictive exhaust
system to contend with. You just might not get the whole 12% of
power boost that you're looking for, and 12% more power is worth
about 4% more speed, if you change nothing else about the
boat.
With an engine this small, the cost of hopping it up to maybe get
5 or 6 HP from it by balancing the rods, shaving the flywheel,
relieving the ports, lowering the head, padding the crankcase,
switching the carb to run on methanol, and so on, will far exceed
the cost of trading it in on a bigger motor. That's my gut
feeling, but I also think it might be a lot of fun ;-) If you're
not into a project like that, I think the lightest current 6 is an
OMC, and the lightest 5 is Merc/Mariner/Nissan/Tohatsu. I doubt
that an 8' aluminum boat is rated for more than 6 hp, if it's
rated even that high.
-- -- Marcus. ( be...@mail.med.upenn.edu )
Paul Webb
My 11 year old son and I use the little Stessl 2.4M Edgetracker tinnie as a
fishing boat usually around the beautiful rivers and inland waterways of
Queensland, Australia. It is a tough (2mm Al), beamy, V nose punt with the
stability of a flat bottom and the cutting advantages of a V bottom. The
reason for the size is that it fits against the wall at the back of my
garage and is small and light enough to put onto roof racks on the Landrover
4WD single handed - there are some bush tracks that could not handle a 4WD
plus boat on trailer.
The reasons for the 1998 Evinrude 4hp short-shaft motor are that it is small
enough to fit easily in the 4WD without need for external tank and light
enough (the lightest for its hp at 15kgs) for the 11 year old to carry.
Another advantage is that in Qld, there is no need to register the boat
every year if the motor is 4hp or under. The setup works well for
estuary/lake fishing but is just a little underpowered so that the boat
almost gets to plane but doesn't.
Speaking of shifting weight around, we get a lot of strange looks from
others. We point the motor straight ahead, set on full throttle, sit on the
bow thwart to reduce bow lift and to steer, move our weight to port or
starboard. We can do full 360 degree turns this way! It's like a motorised
surfboard! My son has a great time!
I think I might research hydrofoils and prop changes to start with. I'll let
you know how it turns out.
Again many thanks for your input. If you have any other ideas, please let me
know.
Cheers
Paul
Lloyd Sumpter <lsum...@home.com> wrote in message
news:387510F9...@home.com...
> I've heard of small boats with 4 hp planing. I never got my 8 ft
> "hydroplane" with 4hp Briggs&Stratton to plane, but there were, well, a
> few design flaws...(and I doubt that that old warhorse B&S was putting
> out 4 hp)
>
> Have you tried all the planing "tricks": jumping on the bow, or
> "waddling" - turning the boat so that essentially one side planes at a
> time.
>
> The bathtubs in the Naniamo Bathtub Race use 7.5hp and plane nicely.
> (they're about 5-6ft long). The top contenders use hydraulics to trim
> the height of the engine. They also use polished 2-blade props. I drove
> one once - they're a ball!
>
> Lloyd Sumpter
> "Far Cove" Cat 36 - bigger than a bathtub
>
> hkr...@capuantispam.net wrote:
> >
> > Paul Webb wrote:
> > >
> > > Dear all
> > > I need a little more power from a 1998 Evinrude 4hp outboard, used on
an
> > > 8ft/2.4M aluminium tender/fishing boat, to get the little boat to
plane (I
> > > don't want a bigger motor or boat). Any suggestions on how this might
be
> > > done as inexpensively and easily as possible?
> > > Many thanks
> > > Paul
> >
Paul Webb
Marcus G Bell <be...@mail.med.upenn.edu> wrote in message
news:853fl2$63o$1...@netnews.upenn.edu...
> Paul Webb (paul...@powerup.com.au) wrote:
> > Dear all I need a little more power from a 1998 Evinrude 4hp
> > outboard, used on an 8ft/2.4M aluminium tender/fishing boat, to
> > get the little boat to plane (I don't want a bigger motor or
> > boat). Any suggestions on how this might be done as
> > inexpensively and easily as possible? Many thanks Paul
>