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

[kg25]

The problem is. He has a boat that is rated for 50hp but is using a 15hp! Think about it. A 15hp is only 30% of the boats max rating. Compare it to a boat that has a max rating of 200hp but it has an 60hp on it. What kind of performance would this rig have? That boat should have a 30 hp at minimum!

I.M.O

I very well may just be underpowered and if that is the case I'll live with it for now. I'll try to make sure the the motor is running like it should and if that helps, great! If not, at least I know I did all I can.

Most of the lakes I go to are pretty small, so I don't have a huge need for a larger motor. I bought this motor because it is an electric start. I had the 9.9 last year, but I have some shoulder issues and the pull start was getting to be a nuisance. I didn't figure out my speed with my 9.9 last year so I can't compare the two.

When I bought the boat, I thought it was just a typica basic 14ft aluminum boat. I thought the 50hp max seemed high for this boat, but didn't think much of it since I am new boater. I wonder what the typical max HP is on 14ft similar boats. If it is lower, do I have a different hull design? Did they have different standards in '68?

[Ice Wolf]

My 14' Alum. Boat is rated at 25hp max. It has a 62" beam and I have a 25hp short shaft Merc on it. It will do 25 - 30 mph. With a hydrofoil it pops up on plane quick. Maybe your boat has a wider beam and maybe it's length is 14' 6" or longer? The 25hp I have is plenty fast all most too fast. But maxing out the hp for the boat it gives good low to mid range power to get up on plane fast under a heavy load.

[MNice]

The problem is. He has a boat that is rated for 50hp but is using a 15hp! Think about it. A 15hp is only 30% of the boats max rating. Compare it to a boat that has a max rating of 200hp but it has an 60hp on it. What kind of performance would this rig have? That boat should have a 30 hp at minimum!

I.M.O

Hard to believe that boat is rated for a 50.. Looks like a WC lund.

[kg25]

If I remember correctly, the beam was somewhere between 60" and 65", but I'd have to measure again for an exact measurement. I never measured actual length, but I'll do that too. The boat has 3 regular bench seats and a small triangle seat in the very front bow.

I am going to take it out this afternoon, so we'll see how the prop does.

Here is a pic of the capacity plate:

[delcecchi]

Remember that in those days they measured HP at the powerhead. So that 50 is more like a 40 today, eg the 4 cylinder merc 2stroke that was the classic fishing motor back in the day.

[MNice]

Holy Carp!! a 50 on that thing would be a blast!!

[Maverick]

It's hard to say without looking, but I would be willing to bet that the boat originally had a center steering column. That would account for the additional horse power rating. Still, a 15hp should do better than it has been doing.

[lotsofish]

I have the exact same boat, except mine is a '73, it's a 16', and it has the 20" transom. Last year I refinished the boat, cutting out the middle seat to add a flat floor, bench seats down the sides, and putting in a raised flat floor in the front. I also put a bow mount trolling motor. I estimate it's added about 200 pounds to the boat (especially weight at the front with the trolling motor and battery).

I have an older 20hp johnson on it and with me, my 3 year old daughter and gear, it goes about 17-18 mph. Also, before I refinished the boat, it was terribly rear weight balanced with just me in it. Taking it out in the wind and anything bigger than 1.5 foot waves was dangerous, because the wind would catch the front and just whip it around.

I suspect something wrong with the motor, and it will be interesting to hear about your results with the other prop.

I don't know if you mentioned it yet, but when you give it full power, does the motor seem like it's revving up to the right speed and it just doesn't move the boat or does it sound bogged down and chugging?

[jentz]

The problem is. He has a boat that is rated for 50hp but is using a 15hp! Think about it. A 15hp is only 30% of the boats max rating. Compare it to a boat that has a max rating of 200hp but it has an 60hp on it. What kind of performance would this rig have? That boat should have a 30 hp at minimum!

I.M.O

If it is a 14ft lund the modern ones are rated 30HP sometimes those spec tags are hard to read.The older lunds are rated 25.So my 14 ft lund screams with a 15 Think about it.Do you have any suggestions for tuning and timing a outboard, its mot the HP rating if you read back posts lunds with 1/2 HP rating move fairly well.

[kg25]

It's hard to say without looking, but I would be willing to bet that the boat originally had a center steering column. That would account for the additional horse power rating. Still, a 15hp should do better than it has been doing.

It is a tiller steering originally. I bought it from the original owner ( a guy in his 70's who had it for 43 yrs). Only thing he changed was adding a floor and making the middle bench seat into a live well. He seemed honest about it and when I repainted everything it was the original red/light green colors and nothing look modified.

[kg25]

I suspect something wrong with the motor, and it will be interesting to hear about your results with the other prop.

I don't know if you mentioned it yet, but when you give it full power, does the motor seem like it's revving up to the right speed and it just doesn't move the boat or does it sound bogged down and chugging?

Ok, so I went on the lake this afternoon with the new prop. Basically had the same results. Bow up high, speed about 6mph. So the prop is probably not spun, unless by some rare chance they both are.

What I did try doing though was to let go of the motor and go sit on the middle bench seat. Very quickly the bow went down and slowly I got it up to about 12mph a couple of times before the motor would turn and I had to go grab the tiller handle. So with me moving up and re-distributing some weight, I got it to go on plane and increase the speed. I don't know if I would have had even more speed increase if I able to keep it straight for longer. Would my speed probably have increased the longer I was on plane?

To my inexperienced ears, the motors seems to rev up to where it should, it just doesn't get me on plane.

So, assuming the motor is running fine (at some point I probably need to get a tach and make sure the rpm's are where they should be), it seems like I might need to just re-distribute weight forward. (unless raising the motor the couple of inches would make a difference in getting on plane?) However, like I said earlier, my 3yr old sometimes comes with and I don't her to be able to mess with the battery or the gas tank so I need to keep this in mind. I either need to build a box she can't access or teach her right away not to touch anything or figure out a way to get on plane as is.

The hydrofoils claim they can get boats on plane quicker for heavy stern boats, is it worth a try so that maybe I don't need to move things around? If I can get it to go on plane with just me in the rear and 12mph or so, I would be happy.

Thanks again for everyone's input! Everyone was new at this at one point right?

[kg25]

My 14' Alum. Boat is rated at 25hp max. It has a 62" beam and I have a 25hp short shaft Merc on it. It will do 25 - 30 mph. With a hydrofoil it pops up on plane quick. Maybe your boat has a wider beam and maybe it's length is 14' 6" or longer? The 25hp I have is plenty fast all most too fast. But maxing out the hp for the boat it gives good low to mid range power to get up on plane fast under a heavy load.

I measured and the beam is 62" and it is 14ft long.

[Surface Tension]

Get the battery and gas tank up toward the bow.

[20lbSloughShark]

yes, if your bow is up in the air it is a ballance issue. Like I said before put some cinder blocks or some other weight up front to keep the front down, I bet this is the problem.

[SkunkedAgain]

kg25 - everyone keeps telling you to distribute the weight better, for good reason. It's likely your main problem right now. For the battery, go buy yourself a cheap battery box (they hold your battery, have space for the cables to come out, and are cinched tight with a strap. Your daughter won't be able to mess with it.

You might also try using a well-capped/locked gas can in the front with only 1/4 tank in the back. That might be a way to carry enough gas but not have it all in the back.

That 15hp likely is a little underpowered considering your weight and the size of the boat. You could weld an aluminum tube onto a transom plate and bolt it all into place. That would probably help with your motor height issue. However, the real problem as others have stated is that you're using the wrong shaft-length motor.

Sell the 15hp, get a 30hp with the right length and shift a little more of that weight forward. You might spend an additional couple hundred dollars on the motor upgrade but you and your family will be much happier in the end.

[Wish-I-Were-Fishn]

I didn't read all the posts, but a stingray hydrofoil would help a lot with the planning issue.

[kg25]

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.

It is a short shaft motor. I know the difference and how to measure the shaft. Without the spacer it is about 1.5 inches below the bottom of the boat. If it was a long shaft motor, it would be 5"+ below, which is not the case.

I also ordered a 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.

[hydro]

KG,

I read through the posts on this thread and would like to add some of my own real world expertise. I have tuned many boat/motor combinations and I think I can help you through this. First, let’s assume that your motor is running correctly and eliminate that issue from the mix. Next, you have a relatively heavy boat and are running a prop specified by the manufacturer for all purpose use, and that is not a match. You mentioned it is a 9.5” dia. X 10” pitch. That is too much pitch and should be replaced by about a 9” max pitch wheel, but it will work for the testing. Your motor should spin right around 6000 RPM at WOT and a lower pitch will help.

You have mentioned that the boat is difficult if not impossible to get up onto plane and several have discussed “balance”. Last weekend you moved weight and crawled up to the middle seat and the boat planed off. There is your balance evidence. Move as much weight as possible up toward the bow (however, DO NOT add more weight!). Get the static balance as far forward as possible since you will be sitting in that rear seat.

As for the motor setup, first get rid of all of those transom height sticks. Raising the motor is a racing trick and will have absolutely no positive effect on your rig once the other problems have been addressed. It can and likely will cause cavitation issues on turns once the planning issue is cured. Your motor is a short shaft and is at the proper height when bolted down without the spacers (I can see that from your pictures).

Assuming the weight distribution issue is under control, adjusting the motor angle is the next step and I suggest moving the adjustment pin into the hole closest to the transom. Take off in the boat and see how much the bow lifts or plows. Repeat this adjustment moving the pin out to the next hole on each subsequent test. Find the best setting and leave it there. At optimum angle with just you in the boat it should plane off in a reasonable time and run with the bow just slightly raised. Too much angle and it will bounce, too little and the bow will plow.

A hydrofoil was mentioned earlier as well and that would probably get the boat up on plane faster (think of it as a lever), but it will cut top speed a little due to drag. I suggest getting the boat working right and then trying the foil to see what it does.

My guess is with that boat and only a 15 HP motor the best you can hope for is to get it to plane out nice and flat and see a top speed of15-18 MPH. That boat with an older 50 HP 4 cyl Mercury motor would maybe get up to 32-35 MPH (I had a very similar combination). Let us know how it works on the next test run!

[kg25]

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.

It is a short shaft motor. I know the difference and how to measure the shaft. Without the spacer it is about 1.5 inches below the bottom of the boat. If it was a long shaft motor, it would be 5"+ below, which is not the case.

I also ordered a 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 a pic of the layout of the boat after I moved the battery in the quoted text above. 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.

[kg25]

KG,

I read through the posts on this thread and would like to add some of my own real world expertise. I have tuned many boat/motor combinations and I think I can help you through this. First, let’s assume that your motor is running correctly and eliminate that issue from the mix. Next, you have a relatively heavy boat and are running a prop specified by the manufacturer for all purpose use, and that is not a match. You mentioned it is a 9.5” dia. X 10” pitch. That is too much pitch and should be replaced by about a 9” max pitch wheel, but it will work for the testing. Your motor should spin right around 6000 RPM at WOT and a lower pitch will help.

You have mentioned that the boat is difficult if not impossible to get up onto plane and several have discussed “balance”. Last weekend you moved weight and crawled up to the middle seat and the boat planed off. There is your balance evidence. Move as much weight as possible up toward the bow (however, DO NOT add more weight!). Get the static balance as far forward as possible since you will be sitting in that rear seat.

As for the motor setup, first get rid of all of those transom height sticks. Raising the motor is a racing trick and will have absolutely no positive effect on your rig once the other problems have been addressed. It can and likely will cause cavitation issues on turns once the planning issue is cured. Your motor is a short shaft and is at the proper height when bolted down without the spacers (I can see that from your pictures).

Assuming the weight distribution issue is under control, adjusting the motor angle is the next step and I suggest moving the adjustment pin into the hole closest to the transom. Take off in the boat and see how much the bow lifts or plows. Repeat this adjustment moving the pin out to the next hole on each subsequent test. Find the best setting and leave it there. At optimum angle with just you in the boat it should plane off in a reasonable time and run with the bow just slightly raised. Too much angle and it will bounce, too little and the bow will plow.

A hydrofoil was mentioned earlier as well and that would probably get the boat up on plane faster (think of it as a lever), but it will cut top speed a little due to drag. I suggest getting the boat working right and then trying the foil to see what it does.

My guess is with that boat and only a 15 HP motor the best you can hope for is to get it to plane out nice and flat and see a top speed of15-18 MPH. That boat with an older 50 HP 4 cyl Mercury motor would maybe get up to 32-35 MPH (I had a very similar combination). Let us know how it works on the next test run!

Thanks for the reply hydro!

In my post just before yours I mentioned I moved the battery up and got it to plane pretty easiliy and got it to 14mph on a short run, so I got some improvement. I used just part of the wood spacer to get the caviation plate about .25" below the boat. I also had the trim in the slot closest to the boat.

The prop on the motor now is a 9.5" diameter and 10" pitch which is what the original service manual says was supplied with the motor. The service manual states other propeller options are 10" diameter x 5" pitch and 9.25" diameter x 8" pitch. Would you suggest either of the alternatives? Or something different altogether? I haven't done enough research yet on props to know how these changes would affect things.

I also ordered a tiny tach over the weekend so at some point I will be able to check rpm's.

Thanks,

[hydro]

Thanks for the interior picture. From that view the boat looks pretty much like a standard 14' Lund, with some additions to the interior. It does not look to have too much excess weight. A healthy 15 HP motor should get it moving fairly well.

If it were me, I would have the existing prop rebuilt (run your spare for now) and see if that improves things. Also take a look at the bottom of the boat, and using a straightedge look for damage in the last 6' or so of hull. If there are bends or damage, that can cause all sorts of issues with planing.

[20lbSloughShark]

I don't suggest a 50 hp on that. My 16' boat has about a 72" beam and is deeper. My 40 scares the hell out of me.

[jentz]

With the pic you put up I can see its a 70s lund,I can tell because 80s lunds have the seat aluminum contoured to the hull.Yours has the spaces where the seat supports meet the hull.I have never seen a 14ft lund rated 50.I dont know about the 16ft what they are rated.My guess is someong replaced the rating tag on that boat.It shows 5 passengers but has 4 seats.The 16 has seating for 5.

[hydro]

Hey 20, have no fear, just drive it like you stole it, smile and wave!

KG- Here is a pic of a boat I had a long time ago that had similar planing issues due to the short 8' length and no way to redistribute weight, except for my butt. I ran a 20 HP motor, spinning a 9 1/2 X 13 two blade prop and it did about 35 MPH. The only way to get it to plane off was to climb out over the front and hang on until the bow leveled and it took off (sound familiar?). Worked the same way with a passenger (note the OH S*** handle behind the seat). Once it planed it was a blast to drive. I just had to get the set-up right. We even pulled skiers behind it, just had to pick them up from another boat with a rope hand off!

[kg25]

With the pic you put up I can see its a 70s lund,I can tell because 80s lunds have the seat aluminum contoured to the hull.Yours has the spaces where the seat supports meet the hull.I have never seen a 14ft lund rated 50.I dont know about the 16ft what they are rated.My guess is someong replaced the rating tag on that boat.It shows 5 passengers but has 4 seats.The 16 has seating for 5.

You're about right for the age...It is registered as a '68 and it doesn't have a HIN, so I know it is prior to November of '72 when a HIN became a requirement. I guess there is possibility the rating tag could have been replaced (it appears to be original), but the guy seemed honest enough about being the only owner and he said he always had smaller outboards, so I don't think he would have switched it to get a higher HP rating. He sold his outboard to a friend, so I bought the trailer and boat only from this guy. His adult son was even there when I bought it and he talked about how he and all his siblings caught there first fish in this boat. But I guess you never know for sure.

Regardless, I don't have a desire to put a 50hp on there. I wonder if capacity and HP ratings were calculated differently in the '60s?