# why won't my boat plane?



## ericman (Jun 26, 2017)

https://www.tinboats.net/forum/viewtopic.php?f=21&t=30830

I did this build a few years ago. Love the boat. Rows great. Stable, yet narrow. Great for motorless lakes. Started hunting the Mississippi River a couple years ago and was a little concerned about hiding my big boat so we hunted out of this with the 3 horse. Long story short. Very long trip back to the landing (upstream). Bought a 7.5 merc. The fin on the lower unit is dead even with the very bottom of the boat. Note that the hull isn't square at the back, it rises up the last 18 inches or so. Again, the fin is dead even with the very bottom, not the bottom at the back. The propeller IS completely under the bottom of the boat. With just myself and 1 other person, it WILL NOT plane. We both weigh 180. Also note how big the center keel is right at the back of the boat.

Is it possible that this part of the keel is diverting so much water that the prop just doesn't have enough water to push. I don't really hear a washy sound like you can if the prop is just up too high. I also just had a new bushing pressed into the prop because it would wind out with one little blade of grass so that part of the equation should be fixed.

Any input would be appreciated.


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## Shaugh (Jun 26, 2017)

You probably just don't have enough horsepower to plane out. My 16 ft alumacraft won't plane with just me in it... with 2 people forget it.... it moves but it will never get going fast enough to get out of the trough...


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## ericman (Jun 27, 2017)

Shaugh said:


> You probably just don't have enough horsepower to plane out. My 16 ft alumacraft won't plane with just me in it... with 2 people forget it.... it moves but it will never get going fast enough to get out of the trough...



I've had an 8 hp evinrude on a 16 foot Lund Bench boat with 2 people plane just fine. That boat was rated for 20 hp. This little Alumacraft is rated for 5.5.

Any other ideas?


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## Shaugh (Jun 27, 2017)

A longer boat will plane more easily with the same total weight.  A small, narrow boat that is heavily loaded starts out deeper in the water and has a smaller wetted surface. That requires more energy to get up and stay on plane.


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## Stumpalump (Jun 27, 2017)

I think it may be the hull with that rounded rear section sucking it down.


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## ericman (Jun 27, 2017)

Stumpalump said:


> I think it may be the hull with that rounded rear section sucking it down.



So, no matter what I do, it will do this?


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## nccatfisher (Jun 27, 2017)

You have way more boat/load than you have motor.


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## ericman (Jun 27, 2017)

nccatfisher said:


> You have way more boat/load than you have motor.




Again, it's rated for 5.5. I have a 7.5 merc that runs awesome. I have used an 8 horse evinrude on 16 foot lunds rated for 20 hp with 2 people that planed just fine. This boat is 13 feet 9 inches long and 46 inches wide. It might weigh 120 pounds. Myself and someone in the front might weight 350. When I used the 8 horse on a 14 foot sears boat it went close to 40 mph.


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## jethro (Jun 27, 2017)

Some hulls just aren't as efficient as others. With a max HP rating of 5.5 I'd say that boat was never designed to plane in the first place. That boat has no beam to give it surface area. You might do better with a hydrofoil to give the motor some lift, but that is a shot in the dark as far as I am concerned.


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## Stumpalump (Jun 27, 2017)

ericman said:


> Stumpalump said:
> 
> 
> > I think it may be the hull with that rounded rear section sucking it down.
> ...



Basically yes. Jethro's hydrofoil may do it. I make my own out of thin aluminum plate but I was thinking a plate on the bottom of the boat to square it up would work. Might not be as hard as you think. They used the same idea on square back canoes with outboards to get the speed up. 







You would just need a flat sheet as wide as the stern and bent at a 90 to rivit to the transome. The metal getting place could cut and bend it cheap enough. It would not have to be a watertight compartment and would drain as soon as you were on plane.


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## RiverBottomOutdoors (Jun 27, 2017)

Not enough HP and the hull is not designed for it either. What you have is a row boat that you can put a motor on to supplement rowing. It was never meant for planning speeds. That is why it has the oversized keel that acts like a skeg; to keep the boat tracking when rowing.


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## nccatfisher (Jun 27, 2017)

ericman said:


> nccatfisher said:
> 
> 
> > You have way more boat/load than you have motor.
> ...


I need to get your formula for getting the best out of a motor. I have a 1448 with a 25 HP on it and I weigh 190# and I get 23MPH by the gps.


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## ericman (Jun 28, 2017)

It seems that maybe the bottom of the hull rising back up to the transom might actually be shooting water right past the motor, preventing enough water from getting to the prop to "jet" me forward. I'm going to make a homemade hydrofoil and try that out. I may also make a 6 inch wide center mounted trim tab for the bottom of the transom if that does not work. I've read several testimonials about hydrofoils on forum.iboats to at least see some promise.

Thanks for all your input.

I will let you all know what my results are next week.


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## Stumpalump (Jun 28, 2017)

That has got to help. What needs to happen on most boats is a clean break from the surface of the water at the transom. A rounded corner keeps the adhesion and sucks the boat down. For example glass boats are made in a mold so a perfect 90 degree corner from the bottom to the transom is not possible. It is ever so slightly rounded to get it out of the mold. On an expensive go fast boats the factory or the bottom blueprinter will grind and reshape this edge to make it as sharp as a piece of cut steel. That alone gives at least a mile or two increase in speed. You are not going 60 but the same principle applies and since your rounded edge is extreme that is a problem. Will a hydrofoil lift the transom hard enough to break this suction? Idk but that's what I'd try because it's easy and this is not a 60 mph boat so who knows what rules really apply. You have closer to what would be called rocker. Rocker/hook/rounded transom all create drag and the faster you go the more it creates. Good luck making sense of all the secretive confusing hull info if you dare to wade into it.


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## Crazyboat (Jun 28, 2017)

So the OP's boat planes with 1 up but not 2 up, am I understanding this correctly? Try adding weight to the boat with just 1 person onboard and see where the engine reaches it's limit to plane.

I'd drop a 10 on back and be done with it, but maybe you feel it's not strong enough, I don't know. Personally pushing 2 guys and gear with a 7.5 is asking quite a bit. I had a 7.5 when I was a kid and I had to shift weight around when my dad rode with me, he was 170 and I was maybe 140. 12' boat that weighted 80 lbs dry.


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## surfman (Jun 29, 2017)

Hull is not designed for planing.


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## ericman (Jun 29, 2017)

Crazyboat said:


> *So the OP's boat planes with 1 up but not 2 up*, am I understanding this correctly? Try adding weight to the boat with just 1 person onboard and see where the engine reaches it's limit to plane.
> 
> I'd drop a 10 on back and be done with it, but maybe you feel it's not strong enough, I don't know. Personally pushing 2 guys and gear with a 7.5 is asking quite a bit. I had a 7.5 when I was a kid and I had to shift weight around when my dad rode with me, he was 170 and I was maybe 140. 12' boat that weighted 80 lbs dry.




I never said the boat planed at all. Result is the same whether myself or someone in the very bow of the boat. Again, if you read my post, you'd see that an 8 horse evinrude pushed a 16 foot Lund rated for 20 horsepower quite nicely with 1 OR 2 people. SO, it would stand to reason that 7.5 horse should be more than adequate horsepower to push a 13' 9" boat that is only rated for 5.5 horse.


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## benjineer (Jun 29, 2017)

I think it should plane, at least with just you in it, but I really don't know the effect of that rounded bottom at the back. I would say check your tilt pin and experiment with different angles there. Typically you plane best with the motor all the way down, but it won't be efficient with the bow plowing down. In your case it may be worse with the whole boat plowing and not enough stern lift. You may have to tilt it up more in line with the angle of the bottom and maybe even raise the motor where the cavitation plate is more in line with the cut off point. It does stand to reason that the boat would want to sag in the back and run deeper because of the reduced buoyancy in the back. Just my opinions. I wouldn't give up on the 7.5 until I had experimented with the angles and position a little more.


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## jethro (Jun 29, 2017)

ericman said:


> I never said the boat planed at all. Result is the same whether myself or someone in the very bow of the boat. Again, if you read my post, you'd see that an 8 horse evinrude pushed a 16 foot Lund rated for 20 horsepower quite nicely with 1 OR 2 people. SO, it would stand to reason that 7.5 horse should be more than adequate horsepower to push a 13' 9" boat that is only rated for 5.5 horse.




You are getting hung up on the size of the boat and the horsepower of the motor. A skilled naval architect can design a 50 foot boat that could plane with a 2hp motor. Fact of the matter is you have a displacement hull that was not designed to plane.


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## Shaugh (Jun 29, 2017)

You can make a trash dumpster plane if you put enough horsepower behind it. But in that boat you are hampered by it's small wetted surface area and a marginal amount of horsepower.

A 7.5 hp motor is on the borderline to plane a boat with 400 lbs loaded in it. I recall my youth and a 12 ft fiberglass Sear Gamefisher with a 7.5 McCulloch ... a heavy pig of a boat, but I could get it to plane if I left the motor and went and hung half my body over the bow for a few seconds.. then I could go back and it would stay on plane. With my 90 lb brother in the boat it would not plane.. ever. There is no magic to getting a boat on plane, but you do need enough surface area and horsepower for any given weight. Adding a fin in back could do it because it will increase your surface area.. that would be the least expensive route... either that or a bigger motor.


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## Stumpalump (Jun 29, 2017)

I'd buy that hull in a heart beat. It's near impossible to find a good boat today that was designed to row. Rowing is a blast because boats go surprisingly fast with little effort. Before you know it you are a mile away. Almost a shame we are helping him turn it into a planing boat.


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## ericman (Jun 29, 2017)

Stumpalump said:


> I'd buy that hull in a heart beat. It's near impossible to find a good boat today that was designed to row. Rowing is a blast because boats go surprisingly fast with little effort. Before you know it you are a mile away. Almost a shame we are helping him turn it into a planing boat.




I actually use it almost exclusively as a row boat when duck hunting. Sometimes I fish from it with the motor. I used to only use the 3 horse evinrude if I planned on going quite some distance. . . .but we ran into an issue when we hunted the Mississippi during a low water period where we needed a smaller boat. . .and it took a really long time to get back to the landing. 3 horse against shipping channel current makes for a very slow actual mph. Got back to the landing and the spare gallon tank was empty and just for kicks I opened up the tank on the motor and didn't even get a reflection from gas in the tank, just a clear view of the bottom. Another 100 yards and we would have had to row to shore and drag it from there. 

My main desire to get this thing up on plane has mostly to do with fuel efficiency and to some extent to save time on trips like above. Just gonna buy a hydrofoil for $30 instead of monkeying around with plate aluminum. Hopefully I'll test by the end of this weekend.


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## RiverBottomOutdoors (Jun 29, 2017)

ericman said:


> Stumpalump said:
> 
> 
> > I'd buy that hull in a heart beat. It's near impossible to find a good boat today that was designed to row. Rowing is a blast because boats go surprisingly fast with little effort. Before you know it you are a mile away. Almost a shame we are helping him turn it into a planing boat.
> ...




Will be interested to see what happens with the hydrofoil. It increases drag so curious if it will perform like you want it. Keep us posted! Good luck.


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## jethro (Jun 29, 2017)

Yeah, that's for sure, my hyrdofoil sucks at least 3-4 mph from my setup but boy does it get up on plane quick.


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## Stumpalump (Jun 29, 2017)

jethro said:


> Yeah, that's for sure, my hyrdofoil sucks at least 3-4 mph from my setup but boy does it get up on plane quick.



You have to ditch that thick plastic drag inducing wing. Nothing performs better than flat plate aluminum. Make it big and cut it smaller to tune it. Too much affects steering. You already have holes drilled and hardware so hack up an old street sign and give it a try. You will get that 3 mph back.


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## Stumpalump (Jun 29, 2017)

ericman said:


> Stumpalump said:
> 
> 
> > I'd buy that hull in a heart beat. It's near impossible to find a good boat today that was designed to row. Rowing is a blast because boats go surprisingly fast with little effort. Before you know it you are a mile away. Almost a shame we are helping him turn it into a planing boat.
> ...



How does it row?


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## Shaugh (Jun 29, 2017)

It's a lot like waterskiing. Once you get up on plane and your speed increases, the amount of energy / speed to keep you there goes way down. I think the wing might work even if it shaves a couple MPH from the top... The trick is to get it out of that trough of water... once you get there you don't need all 7.5 horses...


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## ericman (Jun 29, 2017)

Stumpalump,
The boat rows like a dream. I have 7 foot oars and I made some oar-lock extensions to get the oars up above my legs because I'm sitting so high on the raised benches. I'm considering making new oars, ones with much bigger paddle ends because I feel like I could push the thing even faster. I hunt many motorless lakes and a few that just have too much surface vegetation. ( I won't buy a surface drive, direct drive, mud-motor . . .too loud )

And it really does track and steer well when rowing. It also push poles really fast too. I actually made my push pole out of a 16 foot knot-less cedar 2x4 that I ripped down to 2x3 and rounded the corners. Thing sticks out the back like 4 feet so I have to tie it to the transom handles when I'm going down the road. My hunting partner calls the thing my gondola because I stand on the seat when I'm push-poling. 

I'd like to have a fleet of these old Model B's but you just don't see 'em. I think they made less than 1000 of them in 2-3 years of production. I'd like to make one into a decked layout boat, and I'd like to make one into a strictly small lake fishing boat, you know storage compartments, livewell, battery compartment, 24 volt trolling set-up, etc...


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## WALI4VR (Jun 29, 2017)

ericman said:


> nccatfisher said:
> 
> 
> > You have way more boat/load than you have motor.
> ...


I'm sorry but I call bologna...40 mph...aint happening on this planet

Sent from my XT1650 using Tapatalk


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## Stumpalump (Jun 29, 2017)

ericman said:


> Stumpalump,
> The boat rows like a dream. I have 7 foot oars and I made some oar-lock extensions to get the oars up above my legs because I'm sitting so high on the raised benches. I'm considering making new oars, ones with much bigger paddle ends because I feel like I could push the thing even faster. I hunt many motorless lakes and a few that just have too much surface vegetation. ( I won't buy a surface drive, direct drive, mud-motor . . .too loud )
> 
> And it really does track and steer well when rowing. It also push poles really fast too. I actually made my push pole out of a 16 foot knot-less cedar 2x4 that I ripped down to 2x3 and rounded the corners. Thing sticks out the back like 4 feet so I have to tie it to the transom handles when I'm going down the road. My hunting partner calls the thing my gondola because I stand on the seat when I'm push-poling.
> ...



I made my own push pole as well out of a Home Depot closet rod or stair case railing. Cut to about 12' but that way it fit in my boat. I fit a metal cap on one end so our rocks don't break it and a rubber cap on the other because the wife has a habit of clobbering me with it. I use it to check depth as well in the murky water so I painted black and red stripes on it. Now the wife can tell me when to throw it in neutral and trim up. It's really great the times it's needed. So you have 7" oars? I just bought a set of 6' from a lady selling all her boat stuff. I hope they are not too short for my next small tin? I'm 6'2 so I have some reach. She was a cool old gal that also loved to row. Used them on a trawler dingy. I scored the oars, a chair, a Foldit folding aluminum dock cart and a outboard with a buggered pull cord from her. I could tell she wanted to keep the oars but she knew I wanted them and gave them up. That makes 3 of us that like to row!


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## ericman (Jul 3, 2017)

Problem solved.

Planes out, probably in the 12-14 mph range.


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## ppine (Jul 4, 2017)

No lift with that rounded off transom. It should be square. Not enough power either.


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## ericman (Jul 5, 2017)

See above post.

Problem solved.

See wing attached to motor.

Works good now.


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## RiverBottomOutdoors (Jul 5, 2017)

Is that aftermarket or DIY?


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## ericman (Jul 5, 2017)

DIY 1/8" aluminum plate bent slightly at the rear.


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## RiverBottomOutdoors (Jul 5, 2017)

Nice! Glad you got it worked out.


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## mrdrh99 (Jul 5, 2017)

Nice! I think I may try that with my 9.9


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## RiverBottomOutdoors (Jul 11, 2017)

Keep an eye on your transom. Probably putting a lot more stress on it than it was engineered for.


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