Proper mounting height for 25hp Johnson on a Lund

[Coastalguy]

I have a really well kept 1997 25hp 2cyl Johnson Long shaft on a 1997 Lund SV14 14 ' aluminum 20" transom. I just recently raised the engine about 3/4
inch (one mounting hole) and put a little block on top of the transom. I've yet
to water test but the anti cav plate is now about even with the boats keel
runner and about 1/4 inch below the bottom of the transom. Trying to see if I can correct quite a bit of spray coming from the stern ever since new and see if I can get a little more top end. I've played with the trim seems to make little difference. Top speed at sea level with 2 adults and factory 13" prop was 25 mph as clocked from another boat with a good speedo, before I
raised the outboard.

Any thoughts on this from all you experts? I get alot of different opinions on weather this modification is worthwhile on this type of setup

I appreciate any advice here. Thank you Coastal guy

 

[Expidia]

Re: Proper mounting height for 25hp Johnson on a Lund

I had the same issue when the dealer mounted it too low. I didn't know any better and I had one hell of a rooster tail coming off as spray. So I read here how to try another hole up.

I went up one and then tested it and went up another. It was faster up two holes but it had a steering whip issue so I lowered it a hole again which ended up one hole from where the dealer mounted it.

My Lund manual said OK to have the cav plate 1 inch above the boat's bottom. With motor vertical put a straight edge on the cav plate. Try 1 more hole up. You can always go back down again. Just don't seal the holes with something like 3m 4200 until you are satisfied with the height.

Technically, those lock nuts with the plastic insert are only supposed to be used once. I went back to my dealer and he charged me $5 each (I think) for 4 nuts . So try
HD or Lowes if your "nuts are old"

It's all about the tweaking process. Most dealers don't bother to test drive even a new rig unless they are located on a lake . . . maybe. I paid $700 for a new carb and impeller last year for my daughter's rig at a dealer "on a river" and he never bothered to test drive it. Motor died 5 minutes away from the dock. I had to row back. He had disconnected the hose from the outboard end and I was so ticked off that it died after paying $700, I didn't notice it off. Had to row all the way back to the dock

And welcome to iboats

 

[Coastalguy]

Re: Proper mounting height for 25hp Johnson on a Lund

Thanks for the info. I don't think I will go any higher but do I really need
a block on top of the transom? The outboard has a bolt on each side
( using my original transom holes just moved the motor up one hole) and
the 2 clamps still have a good bite about 1 inch below the transom top.
I planned on replacing both bolts, after a test run and sealing with
good quality silicon ok? Straight edge shows anti cav plate about even
with boat bottom about an inch higher than before, lets hope that helps
minimize the rooster tail.

Than you for responding! coastal guy

 

[Tim Frank]

Re: Proper mounting height for 25hp Johnson on a Lund

I have a really well kept 1997 25hp 2cyl Johnson Long shaft on a 1997 Lund SV14 14 ' aluminum 20" transom. I just recently raised the engine about 3/4
inch (one mounting hole) and put a little block on top of the transom. I've yet
to water test but the anti cav plate is now about even with the boats keel
runner and about 1/4 inch below the bottom of the transom. Trying to see if I can correct quite a bit of spray coming from the stern ever since new and see if I can get a little more top end. I've played with the trim seems to make little difference. Top speed at sea level with 2 adults and factory 13" prop was 25 mph as clocked from another boat with a good speedo, before I
raised the outboard.

Any thoughts on this from all you experts? I get alot of different opinions on weather this modification is worthwhile on this type of setup

I appreciate any advice here. Thank you Coastal guy

If you don't have a tach so that you can get the right range at WOT, you probably wasted your time raising the motor etc.
Just a shot in the dark without knowing if your prop is the right one.

 

[Coastalguy]

Re: Proper mounting height for 25hp Johnson on a Lund

I water tested my 14' Lund SV 14 with a 25hp 2cyl 2 stroke Johnson yesterday after raising the engine 3/4". The anti cav plate is now just about 1/3 inch below the bottom of the transom. At top speed the engine seems to
be turning a bit more RPM than before I raised it but I don't notice any increase
in top end at all. No blowing out on sharp turns or cavitating. Trim is set 1
notch out. I notice a minor improvement in the spray coming off the stern.
MY QUESTION. HOW DO YOU KNOW WHEN YOU HAVE THE MOTOR HEIGHT
JUST RIGHT? Seeing little if any improvement should I just put it back down
with the motor sitting directly atop the transom or leave it alone? I can't raise
it any higher because the hand clamps would then bite into the top of the transom. I'm using my 11 pitch alum prop always recommended for this boat
motor comb at 5200 ft here in Denver
Also does engine height effect the adjustment of the little trim tab on
the back of the anti cav plate?

Thanks guys

 

[Expidia]

Re: Proper mounting height for 25hp Johnson on a Lund

The cav plate is usually supposed to be near the bottom of the transom anyway so if it's handling ok then you might as well keep it where it is.

I'd put a 34 inch block of wood to further support it.

The little trim tab is for steering correction. Mine was pulling to the right when I accelerated so I moved the tab to the left (I think) to compensate and now its good. If you let go of the wheel and the boat tracks to the left or the right then adjust it. They are also sometimes made of an alloy so electrolysis eats into the tab and not your lower drive.

You might also find with more people on the boat it handles better now that the motor is a little higher.

I didn't get more top end when I raised either of my outboards. I did it to lessen the spray due to the lower unit dragging to low in the water.

 

[Coastalguy]

Re: Proper mounting height for 25hp Johnson on a Lund

The final result is I'm leaving the setup as is now with the little
block in place and the motor mounted up one hole and the anti cav plate a hair
less than one inch below the boats bottom. Definitely less spray about the same
top end( maybe a bit better ) and the boat handles better with no front passenger (less bow rise). Can't go up anymore or the clamps will bite too high.
My question for all you Lund experts why does Lund and some other alum
boat companies build these boats with the 20" transom versions just a bit
too low to mount a long shaft outboard right on top of the transom for the
correct motor height?

Got some nice trout this summer anyway with the boat!


Thanks guys

 

[steelespike]

Re: Proper mounting height for 25hp Johnson on a Lund

Transoms are made a touch low so they are sure you can get low enough.
Various motors will run better at different heights and will require different final
installation height.
There a post right now in props new Carolina Skiff 20" transom new 70
20"Suzuki motor.
Mounted all the way down has venting issues both straight and turning.
So it appears sometimes there is a miss match.
As far as your setup I would raise the motor to a point just before venting becomes a problem.Maybe raise the transom.Prop selection can allow more height.
It does seem that 25 is an ok speed for an unrefined setup.
I think a bare bones utility tiller steer could run close to 30 mph.with one aboard.

 

[Coastalguy]

Re: Proper mounting height for 25hp Johnson on a Lund

Thanks for the reply you answered my question on why the transom
is a touch low. When I bought this Lund SV-14 new almost 14 years
ago I saw a spec sheet on a very similar boat with the same engine
and 13 pitch alum prop claimed 25 mph top speed. The 25mph I measured
was at sea level before I raised the engine using my 13" prop and with a
130 lb person up front and me (225) lbs at the tiller. It seems a bit faster
in calm water with just me and just a bit of weight for ballast up front.
The SV series and newer SSV series boats have a mild V hull which I'm
sure slows it down just a bit but they ride pretty well for a small boat
when the water gets rough.
I will be getting a new Lund SSV 16 next year with an E-tech 30. This time
I will have a tach and speedo, and will make sure the engine is mounted at the correct height before i experiment with the prop. This forum is very helpful.
Thanks again coastal guy

 

[steelespike]

Re: Proper mounting height for 25hp Johnson on a Lund

SSV16 and the Etec 30 sounds like a great combination.Is that going to be a basic
tiller steer setup?I feel a console simply adds weight,complication and takes up space.
I think you will find the 16 gets up better with a load and if you could afford the 18 I think would do even better.It would be great to hear about the new boat when you get it.

 

[Coastalguy]

Re: Proper mounting height for 25hp Johnson on a Lund

So refreshing that at least someone knowledgeable agrees with me about
the tiller steer setup, my reasons being the same as yours plus the steering
is much more precise. With just a bit of weight up front I don't think you loose
any top end with these setups either. A guy on here had an SSV-16 with a 40
hp E-tec and he said it purposed due to too much weight in the stern, just a kid
or a dog up front would fix that I bet. The SSV-16 is rated for a 40 max but
I bet that E-tec 30 will be fine for it. It's supposed to be the lightest and most
powerful 30 on the market and I've read they run great. etecownersgroup.com
is loaded with info. The SSV-18 is rated for a 60 so I'm afraid a 30 would be underpowered there and even the SSV-16 will need a fold tongue trailer to go
in a std 18' garage. The 18' won't fit. I want to stick with the 25/30 motor size
because they are so smooth, the larger 40/50/60 hp twin is not as smooth or
slow for trolling.
Thanks for the help Coastal Guy