Boat Planing Problem

[nancur373]

Hey guys. I have a 14' tinny with a 20 yammie FS tiller that I built a casting deck in. It has the two seats across and the two corner seats in the stern. The deck is made from 3/4 plywood and goes from the rearmost bench seat to the stem. It's a full 8' long and like 5' wide at the widest part. It also has a 3/4 ply sub floor in between the two benches. There's a battery in the front with trolling motor. Battery in the rear along with the gas can. With just me in it it gets up on plane no sweat. Me and my 7 and 5 year old boys also gets on plane. But myself and another adult it won't get on plane. I installed a stingray hydrofoil and makes no difference. This motor is fairly new and I would expect it to be able to get up as is with two adults. My uncle has a 14' with a 15 merc and with three lard arses and all gear plus cooler live well goes no problem. When my motor is pushing with two guys it seems to be running at maybe half rpm and wants to pull the tiller away from me to turn right when the steering damper is loose. Any suggestions. Maybe a different prop? It is rated for a 35hp but I would have thought a 20hp would suffice.

Edited July 31, 2014 by PURENEWF

[Bernie]

With the extra added weight of the casting deck and a larger load with your buddy you will need to get a lower pitch propeller.
This allows the engine RPM to develop.

[davey buoy]

Your undersized for the boat.As Bernie said,get a lower pitch prop.That should help you out. Mine I had to drop two sizes to get a half descent plane.

[nancur373]

thanks guys will do

[ecmilley]

Find a local marina with a selection they usually dont mund you trying several out different onesn

Keep an eye on your max rpm as well every degree of pitch is usually 400 rpm increase as a rule

[Fisherman]

Where do you have the trim setting? Try with the trim up one(maybe two) more notch, (prop further away from the rear of the boat) You may be pushing the bow of the boat down right now with the extra weight.

[Sinker]

I would try what fisherman suggested first.

 

Trim up = bow up

Trim down = bow down

 

If that doesnt help, get your buddy sitting closer to the bow and see if it will plane out.

 

A 14fter with a 20 should hop up on plane no problem at all.

 

S.

[porkpie]

I have very deep 14 with a yamaha 20. I can plane out with my family of 4 and a 30lb dog and I do have removable floors, a bow deck and trolling motor in front with battery. I do about 21-22mph with them in the boat, the same with 2 kids out on a tube and me and wife in boat: With myself and fishing gear I get about 25mph and with a buddy I can get 23. All GPS speeds. Weight distribution? I'm not sure what to say, perhaps as suggested try a different pitch prop. I don't have issues planing with my setup and it sounds similar to yours, but you probably have a bit more woodwork.

[mcdougy]

I have very deep 14 with a yamaha 20. I can plane out with my family of 4 and a 30lb dog and I do have removable floors, a bow deck and trolling motor in front with battery. I do about 21-22mph with them in the boat, the same with 2 kids out on a tube and me and wife in boat: With myself and fishing gear I get about 25mph and with a buddy I can get 23. All GPS speeds. Weight distribution? I'm not sure what to say, perhaps as suggested try a different pitch prop. I don't have issues planing with my setup and it sounds similar to yours, but you probably have a bit more woodwork.

 

 

Maybe check your prop pitch for him. It is stamped right on the prop blades generally.

[ecmilley]

Yeah check the trim setting first lol. Assumed you had power trim. My 15 yammy has power trim

[scugpg]

Wow I'm starting to wonder if these yammy 20s are dogs or people just under powering short boats. Any merc owners with similar pain?

 

I too had this setup. 20fs with a 14. Mine had a full floor, casting deck live well, two batteries and a bow mount etc so even heavier than above examples. Played with a couple props and trim settings (should have got power trim) but the biggest help was to ensure the cavitation plate was at level with bottom of boat. The yammys i think are 22.1 inches while most transoms are 20. I raised the motor up along with adding a hydrofoil. Planed easily with 1, but would still plane (though very slowly) even with over 500lbs of people in boat. Topped out at 23mph with 1.

 

Check the height of cav plate in relation to bottom of boat. If it's a lot lower it could be causing excess drag. If you end up raising the transom a bit you would need to do this safely and securely.

Edited July 26, 2014 by Spooled

[porkpie]

I don't find mine to be a dog at all. 25mph by myself is about all I want to do. I'm not sure what peoples expectations are for 20hp motors? A 15hp in good running condition will do about 18mph give or take with 2 fat boys and a days worth of tackle and a cooler in most deep hull 14 foot boats with no woodwork. I think obtaining 23-24 with 2 guys and a load plus some decking is pretty good for a 20. I don't know how much more you can get out of a 20 without modifying it. Anyway, that's a bit off topic, but I don't think low HP Yamahas are suffering performance wise by any stretch.

Edited July 26, 2014 by porkpie

[nancur373]

Thanks for all the suggestions guys. I'll check the cav plate height and also play around with the trim. It's sitting at one from all the way down right now. There are four or five holes to choose from. I'll experiment this weekend

[Sinker]

Mine is set in the middle.

 

S.

[DRIFTER_016]

Mine is set in the middle.

 

S.

 

Mine is set on STUN!!!!

[mcdougy]

Not that this will help you much, but in reply to some suggestions that have been made. I have a small personal experience I can tell. Same boat....two different motors. I have a 14' Starcraft with a factory floor, 4 bench seats in the stern with a full width bench in the front. Live well under one the seats. I believe without digging back into google the boats dry weight is 585 lbs it's a 2007.

 

I first had a 1998 15hp 2 stroke yamaha. With my family (3kids) you would punch it full throttle and in about 45 seconds would achieve full plane with the yamaha working as hard as she can to get there. It would go 18-21 mph at wot. If you let off slightly it would loose plane. It actually works pretty darned good really . To the point that I kept it when I upgraded.

 

My problem with the 15 was I could not get plane with anything past the 5 people or 435 lbs in the boat. Sometimes it would not even get on plane . But in general it usually did. It's a good motor in my opinion.

 

So I upgraded to a brand new merc sea pro 25 h.p. With the same same people the boat planes at about 3/4 throttle and once on plane I can back off to about 5/8 throttle. At wot we get between 25 - 28 mph.

But add much more weight than that and she won't plane. I did the simple carb mod and advanced the timing to make it a 30h.p. and nothing really changed in my opinion.

 

With both motors I played with trim,and lifted the motor off the transom more, nothing seemed to me to make a difference for me.

 

I am now considering a hydrofoil for the 25 to see if that changes much under my big loads.

 

I have not changed a prop before so I cannot comment what differences it makes. But do believe it would make a rpm change which should help.

 

So in short my experience has been. Trim and height of motor have not shown any help. Horsepower definetly has. A prop change should. And a hydrofoil I will report shortly on its effects.

Edited July 31, 2014 by mcdougy

[nancur373]

Mine is set in the middle.

 

S.

I'll play around with it. I just remembered that the transom isn't 90 degree vertical. It is angled. this will also make a difference to the trim

[nancur373]

I have very deep 14 with a yamaha 20. I can plane out with my family of 4 and a 30lb dog and I do have removable floors, a bow deck and trolling motor in front with battery. I do about 21-22mph with them in the boat, the same with 2 kids out on a tube and me and wife in boat: With myself and fishing gear I get about 25mph and with a buddy I can get 23. All GPS speeds. Weight distribution? I'm not sure what to say, perhaps as suggested try a different pitch prop. I don't have issues planing with my setup and it sounds similar to yours, but you probably have a bit more woodwork.

this is the woodwork... went from this...

 

to this...

[Sinker]

I really can't see that making too much difference. I dunno, I can load 10 doz duck decoys and 3 guys in my boat and still get on plane, but that's just my rig. My engine is the max HP for my hull, 40hp.

 

I bet you just have too much weight to the stern when you have the extra people aboard, simply because they are now sitting where the new deck ends, instead of being spaced out more towards the bow.

 

I would think you should hav plenty of power to get on plane with a 14fter with a 20hp engine.

 

S.

[Raf]

i think sinker's right, try shifting weight around, first to the front. even temporarily have your full grown ballast sit right up there..

[nancur373]

I really can't see that making too much difference. I dunno, I can load 10 doz duck decoys and 3 guys in my boat and still get on plane, but that's just my rig. My engine is the max HP for my hull, 40hp.

 

I bet you just have too much weight to the stern when you have the extra people aboard, simply because they are now sitting where the new deck ends, instead of being spaced out more towards the bow.

 

I would think you should hav plenty of power to get on plane with a 14fter with a 20hp engine.

 

S.

If you look where the two batteries are there is a hatch i built to fold up so we can use the front seat while travelling. I had me and battery in the back. My 240lb uncle on what would be the middle seat and my 180lb brother and fuel can on what would be the front seat. I took the trolling motor off the front and the battery for it out. only had three rods and one tackle box. and safety gear was between the two front seats. Even when I had my brother go right up front on the deck it seemed like the boat was ploughing as in the water was coming out from about 3/4 or more the way to the front of the boat...if that makes sense

[davey buoy]

Just make sure your motor is as tight as it can against the transom.You talk about a angle,bring it in as far as it can go.In line with the transom.Should be good.

[Fisherman]

Just make sure your motor is as tight as it can against the transom.You talk about a angle,bring it in as far as it can go.In line with the transom.Should be good.

Ah, me thinks you got it backwards.

[DRIFTER_016]

Ah, me thinks you got it backwards.

 

Yup, the engine needs to tilt up one or two holes on the pin.

Tucking it further into the transom will push the nose down even more increasing the plowing issue.

[Roe Bag]

 

 

Tucking it further into the transom will push the nose down even more increasing the plowing issue.

Had an F20 Yamaha on a 14' tinny. Standard factory supplied prop. I cut a piece of 2X2 the width of the mounting bracket. Placed it under the bracket. This raised the anti cavitation plate so that it was even with the bottom of the boat.The less motor you have in the water the less resistance. Once you find your sweet spot, drill holes and bolt the motor to the transom. In the meantime make sure the thumb screws are good and tight and secure a safety chain.

Three adults and all of our gear it ran out at 17-18 mph. With that load I ran the tilt pin in the third hole up from the bottom. Otherwise, just like Drifter says, the boat is plowing. Solo with my gear I had to lower it to the second hole from the bottom, otherwise the boat would porpoise. I would also intentionally move as much weight forward as possible. This also assisted in preventing porpoising.

Ideally you want as much boat out of the water as possible.

Tilting the motor out and away from the transom forces the back end down and lifts the bow.

Experiment until you find the balance. Once you do I think you will be pleased.