raising 15hp outboard on transom using wood spacer (with pics)

[Texasmark]

Re: raising 15hp outboard on transom using wood spacer (with pics)

Thanks for the reply. I have checked the compression on my own...it was 90psi in both cylinders, which from my understanding is ok since they are about the same. Would the cavitation plate being below the bottom of the boat by 1.5 inches cause it to bog down?

My Merc manual says if compression is below 120 expect problems.....in addition to the even pressure statement.

To each his own, but if that were a 14' flat bottom john then it might pop up. That is a lot of boat for a 15. I had a Mirror Craft 14' with the hull shaped as yours and ran a Merc Mark30 (30 HP) on it with a side console. It ran out real nice. I had an 18 rude I used to run on 14' boats when a teen and it may have gotten to 22ish mph. 6mph smells of trouble. You might get a cheap tach and see where your rpm's are at WOT. That would speak volumes.

Mark

 

[kgronseth]

Re: raising 15hp outboard on transom using wood spacer (with pics)

Thanks again for everyone's input.

OK, I took the advice about re-distributing some weight. Over the weekend I moved the battery to just behind the first bench seat. I also used just part of the wood spacer to raise the motor up a little (the cavitation plate is about .25" below the boat now). I took it out yesterday and things worked out much better. It planed pretty easily, the bow didn't get very high and I got it up to 14mph with me just sitting in the back. I went fishing to a pretty small lake, so I didn't run WOT for super long time, maybe I could have picked up more speed if had more room to run it for longer.

I also ordered a tiny tach so that I can figure out rpms to make sure I am in the right range at WOT. Once that comes I'll test it out and see how the rpms look. If they are in the right range, I can live with the results I got yesterday. If they are off, then I can look to see what I can do to get the motor running right.

Here is the current layout from the above quoted post. The trim is also in the slot closest to the boat. The stern was partially in the garage and I didn't realized the garage would look black. The storage box (I know more weight)was put in by the previous owner and is just the top and front of the box...the sides of the box are the bench seats and there isn't a bottom. (The storage is very nice to have.) I have a 3 gal. gas tank and plan to keep that in the stern for now.

 

[pootnic]

Re: raising 15hp outboard on transom using wood spacer (with pics)

Heres a 9.9hp on a 16' Naden aluminum,it's a pretty big boat.
It's all use at this fishing camp,the guy in the video was pleasantly surprized how well they worked.

 

[foodfisher]

Re: raising 15hp outboard on transom using wood spacer (with pics)

I'm thinking, put that storage box in front of the third seat from the rear, centered so passengers can sit either side. Stored anchor, extra gas and whatnots will go a long way toward leveling the load and help with planeing.

 

[kgronseth]

Re: raising 15hp outboard on transom using wood spacer (with pics)

Look what I just found doing a google search (A pdf brochure of all 1968 Lund boats):
http://www.lundboats.com/pdfs/old-catalogs/1968-alum.pdf

Page 8 has all the specs for 1968 boats! My capacity plate matches exactly to the S-14 Big Fisherman.
The actual pdf might be a bit easier to read, but I copied a couple sections of the brochure.
Centerline = 14'
Beam = 65"
Transom Width = 58"
Depth Amidship = 24"
Depth at Bow = 30"
Hull Thickness = .064"
Approximate Weight = 215lbs
OBC-HP rating, Outboard = 50
Load Capacity, Outboard = 1195lbs
Seats = 4

 

[pootnic]

Re: raising 15hp outboard on transom using wood spacer (with pics)

Nice find.
Funny,if you google Lund boats now,they make 3 styles of 14' aluminums,close to your style.
1 alittle narrower rated 15hp; 2cd one abit wider 25hp and their biggest is only rated at 35hp(pretty sure this 1 was console to).
I don't think yours has any deeper V and it's really light at 215lbs.
I still say it should work fine with a good running 15hp...and I'm alittle crazy but a 50hp on that size boat with a short transom would make me wear a life jacket.
Buy a tach and let us see what the rpms are now that it seems to get on plane.

 

[kgronseth]

Re: raising 15hp outboard on transom using wood spacer (with pics)

Nice find.
Funny,if you google Lund boats now,they make 3 styles of 14' aluminums,close to your style.
1 alittle narrower rated 15hp; 2cd one abit wider 25hp and their biggest is only rated at 35hp(pretty sure this 1 was console to).
I don't think yours has any deeper V and it's really light at 215lbs.
I still say it should work fine with a good running 15hp...and I'm alittle crazy but a 50hp on that size boat with a short transom would make me wear a life jacket.
Buy a tach and let us see what the rpms are now that it seems to get on plane.

Yeah, maybe they were too high with the limits in '68 and lowered them over the years. I looked at a catalog on the site from '72 and basically the same model boat as mine had a 35hp limit and 921lb capacity.

And yes, I ordered a Tiny Tach over the weekend and once I get it I will do the testing on RPM's.

 

[Sea Rider]

Re: raising 15hp outboard on transom using wood spacer (with pics)

The 9.9 HP video just shows a up bow with much hull drag, probably pleases that boater that way, he doesn't know for sure how much fun he's missing by not having that hull on perfect plane. A 15 or higher will do much better definitely. Test this and see if planes better, remove wood shim from transom, center engine propely, sit an adult up front (where anchor is) to have a well front, rear ballanced boat, test trim at 1- 2-3 hole out transom individually at full throttle and check which one gives better results , once correctly set, keeping same passenger/trim last configuration install induction tach, check max wot rpm readings achieved and compare to the max wot rpm parametersthe manufacturer states for that horse, numbers will decide if in need to change prop in case you are under propped.

Happy Boating

 

[kgronseth]

Re: raising 15hp outboard on transom using wood spacer (with pics)

The 9.9 HP video just shows a up bow with much hull drag, probably pleases that boater that way, he doesn't know how for sure how much fun he's missing by not having that hull on perfect plane. A 15 or higher will do much better definitely. Test this and see if planes better, remove wood shim from transom, center engine propely, sit an adult up front (where anchor is) to have a well front, rear ballanced boat, test trim at 1- 2-3 hole out transom individually at full throttle and check which one gives better results , once correctly set, keeping same passenger/trim last configuration install induction tach, check max wot rpm readings achieved and compare to the max wot rpm parametersthe manufacturer states for that horse, numbers will decide if in need to change prop in case you are under propped.

Happy Boating

Thanks for explaining in detail the way of testing. Once I get the Tiny Tach, I'll do the testing.

If I go boating mostly by myself (wife and daughter come sometimes), will the RPM results be skewed at all if testing is done with 2 people in the boat vs the majority of actual use is with 1 person?

Also, isn't having the shim in there to bring the motor up slightly better than having the motor lower? Or are you saying the amount of difference with or without the shim wouldn't have an effect on performance?

 

[pootnic]

Re: raising 15hp outboard on transom using wood spacer (with pics)

Thats whats great about the internet and forums...all kinds of ideas.
What sea rider said may work,only one way to find out.Your outboard should be easy to move around and try different things to,in an afternoon.
For me,I like to get the outboard as high as possible,till it starts to blow out(cavitate?)then lower it a bit.(always make sure it's pumping water,has good flow).Your a big guy,even if you could go above the hull alittle it's going to be in the water once you sit down.
I found the same boat as yours(I think) modded big time(plywood) with a 20hp 4 stroke,maybe ask this guy about his preformance;theres other boats like your here as well...
http://www.tinboats.net/forum/viewtopic.php?f=21&t=26024

 

[kgronseth]

Re: raising 15hp outboard on transom using wood spacer (with pics)

Thats whats great about the internet and forums...all kinds of ideas.
What sea rider said may work,only one way to find out.Your outboard should be easy to move around and try different things to,in an afternoon.
For me,I like to get the outboard as high as possible,till it starts to blow out(cavitate?)then lower it a bit.(always make sure it's pumping water,has good flow).Your a big guy,even if you could go above the hull alittle it's going to be in the water once you sit down.
I found the same boat as yours(I think) modded big time(plywood) with a 20hp 4 stroke,maybe ask this guy about his preformance;theres other boats like your here as well...
http://www.tinboats.net/forum/viewtopic.php?f=21&t=26024

Thanks for the link. Looks like the same boat as mine. I'll see if I can contact him. Plus he lives in the Twin Cities, right where I am.

 

[Sea Rider]

Re: raising 15hp outboard on transom using wood spacer (with pics)

Thanks for explaining in detail the way of testing. Once I get the Tiny Tach, I'll do the testing.

If I go boating mostly by myself (wife and daughter come sometimes), will the RPM results be skewed at all if testing is done with 2 people in the boat vs the majority of actual use is with 1 person?

Also, isn't having the shim in there to bring the motor up slightly better than having the motor lower? Or are you saying the amount of difference with or without the shim wouldn't have an effect on performance?

Some issues to consider :

Short shaft engines normally works best on 15" to 15.5 height transoms, no use giving plain theory if you don't test them under error and trial, what stated on owners manual is just a refference from where to start and not cast in stone as all hull shapes are completely different.

To clear the doubt if that engine will plane the boat satisfactorily go for a wot test with adult passenger siting at bow, make 2 different tests:

(1) Without transom shim, set at correct hole to have engine as pic example 1 & 2 then go wot
(2) With 1/2" height shim, same example as (1) 1 & 2 pics.

In each case, check looking at engine rear which one gives small plate being slightly under water flow, plate must be paralell to water line at plane/wot. Check pics 3-4 for understanding trim and transom heights concepts.

To understand some hydrodinamics, if your engine is poor under at least 50% of the max recommended engine for that boat, you will have excesive hull drag issues, you need an engine with punch that planes boat fast to break initial inertia, triming right and engine height are 2 complete different issues, although they work together hand in hand, they assure best hull slide and top speed performance. keep in mind that with good engine punch boats rises above water line, engine leg accomodates much better and that's what's needed to work properly and have fun as expected.

With one person will have more rpm and less with 2 or 3. Depending on trim/transom engine height, less or more tail/hull drag against water flow, will surely have a notorious effect on overall performance and worst with small engines.

Once engine is correctly trimed, boat well ballanced with correct engine height, place tach and go for a wot spin to check max rpm achieved at full plane and see if in need to change prop to better punch of that small engine. Probably your boat could benefit placing a 4 blade prop ?

Happy Boating

 

[kgronseth]

Re: raising 15hp outboard on transom using wood spacer (with pics)

I got the Tiny Tach and installed it last night. I wasn't able to get to a lake, but I ran it on muffs just to check to make sure the Tiny Tach was setup correctly. I think I got it installed right. I had it in neutral and on the lowest idle on the throttle and it was hovering around 600 rpms. Does that seem about right? Next step is to get on the lake and do some more testing.

 

[Swinerton]

Re: raising 15hp outboard on transom using wood spacer (with pics)

I would have to say the motor is a little down on power for sure. About 20%.

With 2-cycles, a cold piston/cylinder will show higher compression results, than with a warm engine.

Does the manufacturer recommend doing a compression test with a slightly warm motor, or cold?

90psi cold, would be about 75psi warm. Sounds like a worn reed cage, or poor ring sealing if the motor has some wear.


FYI. I took my newly acquired 14' V-hull out today for its maiden fishing trip. It has a 1998 Mercury 9.9hp on it. (2-cycle)

Fully loaded with trolling motor, battery, full 6 gallons of gas, fishing gear, and (2) 200lb persons, I had it going 16mph (GPS) into a 15-20mph HEADWIND..........