To much deadrise?

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Acton

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So I currently own a 9.9 evinrude with this 12 ft rowboat. I've put a lot of work into the motor and I still can't get over 10mph. There are many videos on youtube of guys getting to 20-25mph with the same motor on 12 ft boats. Here is one such video

https://youtu.be/M_OZ4Qa7H9g

I've been told that it's because my boat is a displacement hull and I have to much deadrise near the transom for the boat to properly plane. Is this the case?

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I'm looking at purchasing this 12ft duranatic. It's wide which is what I like, but I want something that'll get up on a plane. It's wider then the boat I have which I hope will provide more stability, but I just don't see how this boat has less "deadrise" then my current boat does. What am I missing? I've been told that the duranatic is a semi-v and will plane at 20mph with my setup. This is according to someone on another forum who claims to have the same exact motor I have with the same exact boat I'm looking at. I asked why these boats are usually advertised as "v-hulls" on craigslist as opposed to something like a jon boat and this was the response I received.

It's not a V-hull. V-hulls are called V's because of the hull shape at the transom. That boat is more or less flat at the transom. However, I have a Duranatic 12 identical to that one and it flat out flies with a 9.9, well over 20 mph. Lot's of Craigslist ads will say V-hull because the sellers have no clue what makes it a V-hull. They see the pointy end and think V-hull. It's the shape at the transom that matters... Back to the Duranautic. I go about 240 myself and my boat handles me just fine. It's relatively shallow, though, so avoid putting all your weight on on transom cap. I usually run with my gas tank between the front and middle seats to balance things out a bit.

This is the duranatic I'm looking at, besides being wider I can't really see how this boat has less "deadrise" then my current boat. What am I missing? I don't want to buy another boat just to have the same issue.

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Unless I am missing something, none of the pictures of your boat show the stern at the bottom????

What was said is correct. A boat that is flat bottomed at the stern has a far better chance of getting up on plane than a rounded or V-bottom at the stern. You may be able to get any boat up on plane with a ton more horsepower...

Please post another picture.

thanks richg99
 
richg99 said:
Unless I am missing something, none of the pictures of your boat show the stern at the bottom????

What was said is correct. A boat that is flat bottomed at the stern has a far better chance of getting up on plane than a rounded or V-bottom at the stern. You may be able to get any boat up on plane with a ton more horsepower...

Please post another picture.

thanks richg99

Do you need a view of the boat flipped over, like the second picture of the duranatic shows? I was hoping that the pictures of the underside of the boat and the transom would be enough. I'll have to take all the gear out of the boat and take the motor off to flip the boat over. Is there any other way I can take a picture of what you would need to see?
 
No, certainly not flipped over. Just a shot from behind the stern...straight on.

From one of the shots, it does appear that the stern bottom is straight across. If that is so, then I don't know what the new boat brings to the table...that you do not already have.

Perhaps your motor isn't putting out full power; perhaps you have to move some weight forward; perhaps you have to adjust the tilt of the motor more "in" towards the transom...

???

richg99
 
The war eagle hull works really good...I have one...but bigger (1548), and a 4 stroke 15 will run about 25 mph at 6100 RPM. Never ran the 9.9 enough to know how fast it would go. Where I used it, you couldn't go any faster than a slow idle anyway. Lot of submerged trees and stumps and booskio's. Mine is on plane by 12mph. At 9 mph its nose up, at 10, it wants to. By 11mph, it's just breaking over. So in my case, if it won't go 10 mph, it won't plane off for the most part.

It takes less power to plane a totally flat hull than it does a semi v or v bottom.....which is one reason the smaller boats are usually flat bottom (as well as many of the river boats, or as we call them trout boats. Totally flat, no ribs. 20 feet long 48" wide, a 9.9 will have it on plane in a couple seconds. That is the way they're designed, to run real shallow. But the bass boat guys, it takes almost all of the 150 hp to get it on plane, once on the pad, it will fly.

Would prop change help you any? A 15hp 'rude should run in the 7000 RPM range, IIRC. Don't be afraid to drop a couple pitch numbers. I have seen (and owned) boats that would NOT plane off. Change to a LOWER pitch prop (from 10 to 9) and that was all it needed. Top speed increased, holeshot improved-drastically- that kind of thing. Some of what I saw was backwards of convetional wisdom.

then I had one boat years ago that would NOT plane, period. 1432 aluminum boat, don't know what brand. I had a 15hp Evinrude on it (electric start too-should've kept it), and it was impossible to plane the hull. I tried a small prop, 4 blade prop, and even a larger pitch and nothing helped. It just plowed water. It wasn't bent up or anything but it just wouldn't plane. I hated it, and it was a pretty light hull that I carried in the back of my El Camino. Load the motor into the back of the boat (not on the transom, just in the back for weight), slide the boat into the truck, or cark or cruk whatever people call those things, throw the tank, line, and tackle in and head to the lake on lunch break.
 
I don't think I'd pay too much attention to your first advice...I also find his claims of MPH a bit suspect. I'd call your boat a rowboat too but it is also exactly the same kind of boat that thousands of ma and pa resorts used as rentals back in the day...and they still may...but usually those would have maybe a 15 HP tiller motor on them. (I learned how to waterski on one just like that when I was a kid.) I would say that you are expecting too much from that much boat and a 9.9 motor, especially when you load it with cooler and gear. Does the boat have a capacity plate on the transom telling you what the max HP should be? I suspect you could put a 15 or 20 on it and it would get up on plane with your stuff in it nicely. One other thing: no two old aluminum boats are the same so comparing them with expectations is almost an exercise in futility.
 
momule said:
I don't think I'd pay too much attention to your first advice...I also find his claims of MPH a bit suspect. I'd call your boat a rowboat too but it is also exactly the same kind of boat that thousands of ma and pa resorts used as rentals back in the day...and they still may...but usually those would have maybe a 15 HP tiller motor on them. (I learned how to waterski on one just like that when I was a kid.) I would say that you are expecting too much from that much boat and a 9.9 motor, especially when you load it with cooler and gear. Does the boat have a capacity plate on the transom telling you what the max HP should be? I suspect you could put a 15 or 20 on it and it would get up on plane with your stuff in it nicely. One other thing: no two old aluminum boats are the same so comparing them with expectations is almost an exercise in futility.
^^^^^^
This is what I was thinking, but was waiting to see if someone else said it first. I find it really hard to believe that a 9.9 would push a 12' boat "well over 20 mph" as stated. 12 to 15 maybe...

Also the headliner on the video you posted claimed it was a 9.9 converted to a 15...

2015 Tracker Grizzly 1448 MVX
1996 Evinrude 25hp 3 cylinder looper
 
Acton said:
So I currently own a 9.9 evinrude with this 12 ft rowboat. I've put a lot of work into the motor and I still can't get over 10mph. There are many videos on youtube of guys getting to 20-25mph with the same motor on 12 ft boats. Here is one such video

https://youtu.be/M_OZ4Qa7H9g

I've been told that it's because my boat is a displacement hull and I have to much deadrise near the transom for the boat to properly plane. Is this the case?

977l6x.jpg
r72gip.jpg


dcyi5i.jpg
fllyer.jpg
2gy2jx1.jpg


I'm looking at purchasing this 12ft duranatic. It's wide which is what I like, but I want something that'll get up on a plane. It's wider then the boat I have which I hope will provide more stability, but I just don't see how this boat has less "deadrise" then my current boat does. What am I missing? I've been told that the duranatic is a semi-v and will plane at 20mph with my setup. This is according to someone on another forum who claims to have the same exact motor I have with the same exact boat I'm looking at. I asked why these boats are usually advertised as "v-hulls" on craigslist as opposed to something like a jon boat and this was the response I received.

It's not a V-hull. V-hulls are called V's because of the hull shape at the transom. That boat is more or less flat at the transom. However, I have a Duranatic 12 identical to that one and it flat out flies with a 9.9, well over 20 mph. Lot's of Craigslist ads will say V-hull because the sellers have no clue what makes it a V-hull. They see the pointy end and think V-hull. It's the shape at the transom that matters... Back to the Duranautic. I go about 240 myself and my boat handles me just fine. It's relatively shallow, though, so avoid putting all your weight on on transom cap. I usually run with my gas tank between the front and middle seats to balance things out a bit.

This is the duranatic I'm looking at, besides being wider I can't really see how this boat has less "deadrise" then my current boat. What am I missing? I don't want to buy another boat just to have the same issue.

53p74k.jpg
2hrivpf.jpg

In the video the motor was modded by adding a 15 h.p. carburetor.
Your rating plate should indicate 10 or 15 H.P. max on your boat.
You get near or at max ,then she should more likely plane.
 
My motor is also a 9.9 converted to a 15, I should have mentioned that in the original post. A 9.9 converted to a 15 isn't a TRUE 15 because they have two different exhaust pipes.

In this video the guy does a before and after speed test for a converted 9.9 johnson. 9.9 johnsons and evinrudes are the exact same motors internally fyi. Even with the boat fully loaded at 540lbs BEFORE the conversion he gets up to 13.4 mph. With just him and the boat he gets 22.5 mph.

https://www.youtube.com/watch?v=7D0_szcNa6Q

After the carb conversion with the fully loaded at 540 lbs he gets up to 21.1 mph. With just him in the boat he gets up to 25 mph.

https://www.youtube.com/watch?v=7D0_szcNa6Q

I did buy another boat, I will post pictures when I take them. At this point I bought a new 4 blade 9.25 dia x 8" pitch prop since I've seen claims in topics elsewhere that people have seen improvements in speed switching from a 3 blade to 4 blade prop. I've ordered a tiny tach to measure rpms, and I plan on using dunk's method to decarb the motor with seafoam. After that I'll see where I get the best rpms at what trim level. Apparently I should be getting 5500-6500 rpms at WOT.

I've already put a lot of money into the engine previously, so I'm not sure what I'll do if none of this works. Just a few of the things I've done to this engine include installing a new carb kit and giving it a thorough cleaning, which included replacing the welsh plugs, and synching the cam roller to the cam properly so the throttle plate opens appropriately at WOT. I've installed a new fuel pump, and I replaced the head gasket. I've got 93psi on both cylinders. I know some of you guys will bring up the compression, but just like with how fast a 9.9 converted to a 15 can get you, compression numbers on these older outboards seem to be something that people can't come to a consensus on. I've been told elsewhere that others have similar compression numbers on their outboards and get similar mph readings as in the video above.
 
Diameter and pitch being the same or close to, you will see a slight decrease in speed going from 3 blade to 4 blade. You may notice it'll be smoother and may give you more stern lift/plane quicker.

2015 Tracker Grizzly 1448 MVX
1996 Evinrude 25hp 3 cylinder looper
 

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