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

[kg25]

I recently bought a '77 15hp Evinrude electric start motor. I have it on a 14ft modified V '68 Lund that I bought last year (see pic from last summer after I repainted it - a different motor is in the pic) . It is a 15" transom and a short shaft motot. I am only getting about 6mph with the motor with myself (250lbs), battery, trolling motor, gas tank, anchor and gear. The boat also has flat floor and live well added by the previous owner. I feel like I should be getting more speed. This is my first boat so I don't have a lot of experience. I noticed today the the cavitation plate was about 1.5 inches below the bottom of the boat (back of the boat is flat, straight across.)

The motor is held on the the transom with 2 clamps and I saw that I had about 1.25 inches that I could move them up and still be clamped to the transom. I used some wood ( see attached picture) I had laying around as a spacer for the motor mount to sit on. You can see in the pic that it is still clamped onto the original transom and see marks left from the previous position of the clamps. Raising it up now puts the cavitation plate about .25 inches below the bottom of the boat.

My questions:

1. Is it ok to use the wood spacer either temporarily or permanently? If not, What would be good permanent solution?

2. Will this increase my speed? (I obviously won't be going super fast, just want to get what I can out of the motor)

3. The bow also rides high when it is just myself, will this help? ( I know I could move some things to the front to redistribute the weight better, but we bring my 3 yr old daughter with sometimes and I don't her to be able to mess around with a battery/gas tank)

4. Would adding a hydrofoil to the engine be beneficial (for speed and the bow being high)? (I see they are pretty cheap)

Thanks!

[BoxMN]

I think I might try to get a decent piece of angle iron to help hold it, myself. That just seems like the torque might try to work itself loose eventually... or at least tie the "blocks" into a piece of plywood that goes down below the clamps, to try to make it into one larger piece.

But aside from that, with a 15hp I would think you should be planing no problem, which makes me wonder if you might have a spun hub. i.e. rpm's still get high, but prop is not biting cause it is spinning on shaft. You can bring prop to prop guy/shop and they can tell you if that is it.

Good luck! The 15hp should have that boat hauling azz

[jentz]

Your pushing the limit with the motor clamps so close to the top of the transom!!! What is the norm reccomendation for bottom of boat in relation to the calivation plate is even with bottom of hull.I have found 1 inch below is better than even.Its also reccomended not to go more than 1 inch below.

I think your problem may be in the boat itself.The spray foam flotation in boats Absorbes water! I will bet your flotation is saturated and adding excessive weight.

My 14ft lund had saturated foam in the tune of close to 340 lbs and it wasnt all saturated.I replaced it and with a 1988 15HP evenrude it flys! cant qoute a speed but it picked up at least twice speed and planes out great NOW.

I should add my brother in law showed me the problem and helped me get it up and running right!

[mallardnwalleye]

Your trying to make a silk purse out of a sows ear (the motor match not the boat). Either buy a jackplate for the long shaft and bolt it into your nicely restored boat or buy a short shaft out board. Your jury rigging with trepadations-that never works well mechanically speaking. Spend the money and make it functional or you will spend gobs of time and eventually the money by not comitting to the boats fuctionality.

Nice job on the paint!-I would have never guessed it was a 68.

[kg25]

I think I might try to get a decent piece of angle iron to help hold it, myself. That just seems like the torque might try to work itself loose eventually... or at least tie the "blocks" into a piece of plywood that goes down below the clamps, to try to make it into one larger piece.

But aside from that, with a 15hp I would think you should be planing no problem, which makes me wonder if you might have a spun hub. i.e. rpm's still get high, but prop is not biting cause it is spinning on shaft. You can bring prop to prop guy/shop and they can tell you if that is it.

Good luck! The 15hp should have that boat hauling azz

Thanks for the reply. There is a little lip right above the clamp so I think that will help a little, but a more permanent solution would be good if I keep it this way. I might tie a safety rope to it when testing it just in case.

Edit to add: I'll check out the spun prop idea too.

[kg25]

Your pushing the limit with the motor clamps so close to the top of the transom!!! What is the norm reccomendation for bottom of boat in relation to the calivation plate is even with bottom of hull.I have found 1 inch below is better than even.Its also reccomended not to go more than 1 inch below.

I think your problem may be in the boat itself.The spray foam flotation in boats Absorbes water! I will bet your flotation is saturated and adding excessive weight.

My 14ft lund had saturated foam in the tune of close to 340 lbs and it wasnt all saturated.I replaced it and with a 1988 15HP evenrude it flys! cant qoute a speed but it picked up at least twice speed and planes out great NOW.

I should add my brother in law showed me the problem and helped me get it up and running right!

Thanks for the reply. This is just your typical aluminum bench seat/ aluminum floor Lund with the flotation in the bench seats (which are dry - I opened the seats when repainting it). The floor was added by the previous owner to make it easier for him to stand and there isn't any floatation/foam under the floor. He was in his 70's and the original owner of the '68 boat. He also converted the middle bench to a livewell. The floor and livewell were both done by a marina. Both of those added some weight to the boat, but not like waterlogged foam which you are referring to. I understand what you are saying though.

[kg25]

Your trying to make a silk purse out of a sows ear (the motor match not the boat). Either buy a jackplate for the long shaft and bolt it into your nicely restored boat or buy a short shaft out board. Your jury rigging with trepadations-that never works well mechanically speaking. Spend the money and make it functional or you will spend gobs of time and eventually the money by not comitting to the boats fuctionality.

Nice job on the paint!-I would have never guessed it was a 68.

Thanks for the reply. It actually is a short shaft motor and it is a 15" transom. The shaft is actually just a little longer than a typical short shaft by an inch or so, which is why my motor sits a bit low. After doing a bit of research, some of the older Evinrudes were like that with the shaft lengths. It is not a long shaft because there is not an extension in the lower unit, plus it would be more like a 5" difference. I am going to post a couple more pics of the motor so you can it more clearly.

Thanks for the compliment on the paint job! It was a lot of work (sanding, priming, painting, etc) but it turned out pretty good for my first time doing it. I got a lot of knowledge from the Iboats restoration forums.

[kg25]

Here are a couple more pics of the motor with the wood spacer in there, but it is still about .25 inches below the boat. I was able to raise it about 1.25 inches with the spacer. The lighting isn't the greatest since it was raining and I had to take them in the garage.

[Maverick]

I wouldn't mess with the motor mount at all. Your lund and the old 15hp Johnson/Evinrudes were pretty good matches. My buddy and I had similar setups. Besides, you are dealing with a 15hp motor, not a high performance machine. I think part of your problem maybe related to your prop. It is very beat up and might not be the original diameter and pitch. It could be spinning, that was pretty common back then. The other thing is, though, a 15 hp motor with your boat without all of the additions would work pretty well. But, you have a floor, livewell, battery,etc. You have added a lot of weight. I think it is possibly underpowered to the point that you can't get up on plane. That would keep you around 10mph. I just can't imagine that moving the motor up or down an inch or two would make that much difference in a 15hp motor.

[Maverick]

One more thing. You say that the bow rides high when you are alone. That means you are pushing a lot of water. try moving the battery forward and maybe the gas tank. Also, try moveing the bar that adjusts the angle of the motor on the transom so the motor sits closer to the transom. That should lower your bow on take off and might help get on plane. Best of luck.

[Ice Wolf]

I would remove the wood and let that motor sit all the way down on transom. Move tilt trim pin all the way down. ( last hole ). That will lower your bow down when going forward. What is the max motor size for that boat? That motor you have might not be a good match for your boat? I have a 14' Alum boat with a 25 hp merc. A late 80s model. That will do 25 - 30 mph. It's the max motor size for that boat. Your boat looks very nice! Good luck with the motor.

[kg25]

Thanks for the additional replies. I may very well be underpowered. The capacity plate states a max of 50hp and max capacity of 1195 lbs. (Although looking at the boat, I can't imagine using a 50hp on it).

The additional pics I posted last night have the trim pin in the 2nd slot, I have been using it in the 1st spot closest to the boat. I was messing around with the trim last night and took the pics with it in the 2nd slot.

I know I could redistribute the weight by moving the battery and gas tank forward, but sometimes my 3 yr old daughter and wife come along and I don't want to have my daughter to have access to mess with the battery or tank. I'd rather deal with the issues of having the weight in the back than move those items forward for now.

So with that being said...if I am underpowered and the bow rises, do I have any options to improve performance with my current setup? Getting a different motor isn't an option at this point.

Would a hydrofoil added to the cavitation plate on the motor be benefical in my case? I have read that those help to keep the bow down which would be nice when I am in the boat alone.

Edit to add: I also have a '81 9.9 Evinrude with the same size prop as I have on the 15hp. It looks to be in better shape, so maybe I should put that prop on the 15hp? That looks like it is pretty easy to do, any tricks to changing a prop?

Thanks for all the input.

[Ice Wolf]

A hydrofoil would deffently help. I have one on my boat and it works great! I think it's a Dolphin brand. You might want to check to see what prop choices you have for that motor and try a different pitch. Maybe the prop that's on the motor is the wrong size altogether ? Call a marine dealer and give them the ser# and see what choices they give you for prop size and pitch. If your boat states that max hp is 50 than your 15 hp is way under powered and staying with the 15 hp you can't expect much performance out of this set up.

[kg25]

A hydrofoil would deffently help. I have one on my boat and it works great! I think it's a Dolphin brand. You might want to check to see what prop choices you have for that motor and try a different pitch. Maybe the prop that's on the motor is the wrong size altogether ? Call a marine dealer and give them the ser# and see what choices they give you for prop size and pitch. If your boat states that max hp is 50 than your 15 hp is way under powered and staying with the 15 hp you can't expect much performance out of this set up.

I was looking around and saw the Doel Fin hydrofoil for $30 at amazon. I think I will give it a try, it can't hurt and I can always remove it.

I have an original service manual for the motor and found the prop info. The prop on the motor now is a 9.5" diameter and 10" pitch which is what the 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. I haven't done any research as to how the other props might change things.

[MNice]

KG25, something doesn't add up at all. I had a 14' lund with a factory flat floor, 15 horse mariner and I could get 18-19 MPH with just me in the boat according to GPS (6-2 about 220). Distribute weight to front, like battery and maybe even gas tank, should keep the bow down. Couple of other things to check.. Sure your prop isn't spun? Sound like motor is getting up to proper rpm? Prop right size & pitch? I would have to guess the motor height has nothing to do with your problem.

good luck

[kg25]

KG25, something doesn't add up at all. I had a 14' lund with a factory flat floor, 15 horse mariner and I could get 18-19 MPH with just me in the boat according to GPS (6-2 about 220). Distribute weight to front, like battery and maybe even gas tank, should keep the bow down. Couple of other things to check.. Sure your prop isn't spun? Sound like motor is getting up to proper rpm? Prop right size & pitch? I would have to guess the motor height has nothing to do with your problem.

good luck

Thanks MNice. Yeah I am posting at a different site as well and some are suggesting I check to make sure it is running on both cylinders. So I plan to do a spark test to make sure.

Per the service manual, the prop is the correct size, but I will look into it being spun.

Like I said in a previous post, I also have an '81 9.9hp Evinrude with the exact same prop. Can I just put that one on the 15hp? Is it easy to swap out? I need to research what actually is "spun" on a spun prop and see if just swapping the prop from my other motor will work or if I need replacement parts of some sort.

I am getting conflicting opinions, some say I am just underpowered and not much I can do and others says I should have enough power. I'll just keep checking things and eliminate possible things that are wrong.

[BoxMN]

Good luck kg, but I will stick with my thought of spun hub. Basically there is a rubber core in the prop, that acts like a shear pin on the older motors. It is a protection for the motor. This can get old, hard, slippery, or broke, and then once the rpms get high enough, the friction is lost, and the prop "spins" on the "hub". Thus spun hub On props that small, you will likly need a new prop if this is it. On larger props the hub is a separate part of the prop assembly and you can just get a new hub. So if you can troll fine, motor seems to be starting, runnning, fine, and you can actually get high/normal rpms, then my guess is spun hub

Good luck, hope you find the prob and get out on the water and flying soon. I agree that a 15hp on that boat should push it nice with one or two people in it. Not speed records, but plenty fast to get a grin on your face.

[kg25]

Good luck kg, but I will stick with my thought of spun hub. Basically there is a rubber core in the prop, that acts like a shear pin on the older motors. It is a protection for the motor. This can get old, hard, slippery, or broke, and then once the rpms get high enough, the friction is lost, and the prop "spins" on the "hub". Thus spun hub On props that small, you will likly need a new prop if this is it. On larger props the hub is a separate part of the prop assembly and you can just get a new hub. So if you can troll fine, motor seems to be starting, runnning, fine, and you can actually get high/normal rpms, then my guess is spun hub

Good luck, hope you find the prob and get out on the water and flying soon. I agree that a 15hp on that boat should push it nice with one or two people in it. Not speed records, but plenty fast to get a grin on your face.

Thanks BoxMN! The description helps a lot, I wasn't sure if the spun part was part of the prop or a different piece. Since I have an '81 9.9 Evinrude with the exact same prop as the 15hp (plus the other prop is in better condition), I should be able to just swap the props and keep the same washers, nut, etc. currently on the 15hp?

Tonight I would like to the swap props and test to make sure it is running on both cylinders. If it is running on both cylinders, I'll take it to the lake and see if the different prop makes a difference. That should help me get a better perspective.

It starts fine, idles fine, has 90psi compression in both cylinders so it is a decent motor for its age.

Thanks again everyone for your input! It is greatly appreciated.

[kg25]

I was able to test tonight that it is running on both cylinders, so that is good news. I also put my prop from my '81 9.9 Evinrude on the 15hp. So my next step will be to lake test it (without the wood spacer) and see if the old prop was spun. I will report back the results and and go from there.

Thanks again for everyone's input!

[20lbSloughShark]

I used to use an 18 hp on a 16' boat (its much bigger than that one and rated up to 50 hp and 1300 pounds. The 40 hp on it now is just about perfect, a 50 on yours would just be stupid). Anyway, your problem is probably just balance. When alone I put 2 cinder blocks in the front to keep it down. The problem is that when all the weight is in back, the motor has to push you up and forward to plane. With weight in the front it only has to beat the drag of the water, and should plane fine. I would expect about 15 mph with that combo. Don't raise the motor up, you will only ventilate (suck air causing you not to move, basically like a short shaft on a 20" transom).

[MNice]

KG, you may even try the boat with the 9.9 on it...nothing to lose. I'm not sure, but 90 psi sounds a little low, but I could very well be wrong. good luck

[jentz]

90 PSI on both cylinders is just fine.If they had 10% or more compression difference then it would be a problem.No spun prop,both cylinders fireing.caltivation plate looks fine (altho I would remove the spacer)

My 14 ft lund with a 88 15 evinrude,split 2nd seat with a size 29 battery in each compartment 2 batts 6gal.fuel tank under rear seat,factory flat floor me and the betterhalf in it ran at 18MPH just last evening.

Cant even think of a problem you should have! Maybe the prop off the 9 will tell the tale??? Hope you get it.

A spun prop would let the motor rev super high at high speed may even sound as if the motor is going to blow

[jentz]

I dont know how you determined that both cylinders are fireing,Just looking for spark may give a false positive.The best way is with the motor running pull a plug wire off a plug.Say you pull the top wire and it keeps running,You then know the bottom hole is fireing,Then replace it and pull the bottom plug wire,If it keeps running the top hole is fireing.But if you pull one and it kills then the other cylinder is not fireing.Looking for spark may show spark but when its under compression the plug may not fire.It could be a weak coil,bad plug,plug wire.How did you test for both cylinders fireing?

[kg25]

I dont know how you determined that both cylinders are fireing,Just looking for spark may give a false positive.The best way is with the motor running pull a plug wire off a plug.Say you pull the top wire and it keeps running,You then know the bottom hole is fireing,Then replace it and pull the bottom plug wire,If it keeps running the top hole is fireing.But if you pull one and it kills then the other cylinder is not fireing.Looking for spark may show spark but when its under compression the plug may not fire.It could be a weak coil,bad plug,plug wire.How did you test for both cylinders fireing?

Thanks for the reply jentz!

This is what I did. Using muffs, I ran it on idle for about 5 minutes with both plug wires attached. I then stopped the motor, removed upper plug wire and ground it. Motor started right up and I could tell it was not as strong as with both plugs. Then I did the same thing with the lower plug wire and got the same result. So each cylinder started up on its own. Someone on a different forum suggested I test it this way.

Hopefully the prop will be the issue. If not, I'll keep trying. Getting a tach and figuring out rpm's was also suggested on the other site, so I can look into that too if the prop doesn't help.

[Ice Wolf]

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