Too much "deadrise"?

[Acton]

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?

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 from another topic 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.

 

[airshot]

Lots of things can affect overall speed, you sure that is a 12' er? looks longer in the pic....Someone would be really asking a lot to get 25 mpg with a 9.9, I had one in 94 on a 12' river jon boat and could only get 18mph with an almost brand new motor. My 14' would just barely get on plane with just me in it until I converted it to 15hp then at best was 21mph. If the hull is smooth, not rough, and there is no hook in the hull then I would take a serious look at your motor performance and the prop. Even with everything in prime condition mabey 20-21 mph but I would not expect 25.

 

[Acton]

No Title

Well it is a 9.9 with a 15hp carb in it. It doesn't have the same exhaust as a 15 though which I've been told affects the horse power so I just call it a 9.9. My boat is a little under 12. Here is another pic from when I bought the boat off craigslist.

In the other topic I made I was advised to get a 8" 4 blade prop and to run seafoam through the engine which are the other two things I plan to do to boost performance. In this case I'm wondering if investing in another boat would be worth it as well in regards to the whole "deadrise/displacement hull vs planning hull" thing.

 

[fhhuber]

Balance of weight, angle of the engine, total weight, getting the correct depth of the anti-vent plate....

Engine angle is not so fine an adjustment on those unless you want to play with wedge inserts which are a real pain in the neck.
Push the adjustment pin one hole further from the transom maybe.... (maybe) That will lift the nose more if you have the front end of the boat a bit heavy. The engine driving the nose down will slow you down.
Best angle is JUST pushing the nose down from where it bounces a lot. Its slower than the bouncing nose but you have better control of the boat. If 10 lb anchor being moved from by the transom to the front of the boat cures the bouncing nose its perfect right there.

Need a pic more from the side almost making the anti-vent plate look like a line. Should see the whole prop and about the back 1/8 of the hull.
I think your engine may be too long shaft for the transom its currently on.
Anti vent plate should be even with or very slightly below the bottom of the transom.

With these light aluminum hulls... the higher sides mainly let you carry more weight and handle bigger waves.

 

[rallyart]

It doesn't look to me like it has too much deadrise. It does look a little like it might be a displacement hull but I'd need to see better pictures of the shape. If it is a displacement hull it should be very efficient and need little power to cruise slowly but planing can be tougher. A displacement hull will get sucked into the water rather than getting on plane with speed. The cure for that is adding 'hook' or something like smart tabs to break the suction at the stern and give lift. A displacement hull will narrow and curve up some as it approaches the transom.

The duramatic in the lower photos looks to have a straight line for the hull from about a third of the way back. Nothing there will suck the boat into the water.

 

[Acton]

It doesn't look to me like it has too much deadrise. It does look a little like it might be a displacement hull but I'd need to see better pictures of the shape. If it is a displacement hull it should be very efficient and need little power to cruise slowly but planing can be tougher. A displacement hull will get sucked into the water rather than getting on plane with speed. The cure for that is adding 'hook' or something like smart tabs to break the suction at the stern and give lift. A displacement hull will narrow and curve up some as it approaches the transom.

The duramatic in the lower photos looks to have a straight line for the hull from about a third of the way back. Nothing there will suck the boat into the water.

I did some research and found this picture on how to "hook" the hull as rallyart mentioned above. This might be the solution for me. I weight 275 and the stern of the boat sits pretty low in the water. I've tried putting weight in the front of the boat, even having my fiance sit up in the front seems to make little difference in performance. I've also tried the next notch up with the trim and I went slower.

I will post more pictures of the underside of my hull as soon as possible. The person I'd be potentially buying the duranautic from would be willing to take my boat as partial credit for this one, but I'd prefer to hold onto my money if there's no real benefit to moving to a new boat.

 

[JoLin]

I will post more pictures of the underside of my hull as soon as possible. The person I'd be potentially buying the duranautic from would be willing to take my boat as partial credit for this one, but I'd prefer to hold onto my money if there's no real benefit to moving to a new boat.

Need a straight-on shot of the transom of the boat to see if the bottom at the stern is flat, V'd or curved. The response you got regarding the definition of a v-hull is pretty much correct. The Duranautic in the pic is what was referred to back in the day (1960's) as a 'semi-V' hull. V'd at the bow, flattening at the stern to a planing surface. It was the norm for pleasure boats up to 20' or so, because we didn't have the outboard power we have now. My Dad ran our 17' semi-v runabout with a Johnson 40 and a load of kids. That setup was typical for a boat that size. Took awhile, but we could plane out and hit 20-something mph.

If it come down to it, I'd replace the boat rather than redesign it. Right now it's worth some money. IMO, if you go monkeying around according to a 'guesstimate' you're likely to ruin the hull.

My .02

 

[Acton]

Need a straight-on shot of the transom of the boat to see if the bottom at the stern is flat, V'd or curved. The response you got regarding the definition of a v-hull is pretty much correct. The Duranautic in the pic is what was referred to back in the day (1960's) as a 'semi-V' hull. V'd at the bow, flattening at the stern to a planing surface. It was the norm for pleasure boats up to 20' or so, because we didn't have the outboard power we have now. My Dad ran our 17' semi-v runabout with a Johnson 40 and a load of kids. That setup was typical for a boat that size. Took awhile, but we could plane out and hit 20-something mph.

If it come down to it, I'd replace the boat rather than redesign it. Right now it's worth some money. IMO, if you go monkeying around according to a 'guesstimate' you're likely to ruin the hull.

My .02

Yeah I think I'm just going to go with the duraunatic, decarb the engine with seafoam using dunks method plus spraying seafoam deep creep down the spark plug holes and going with a Solas 4 blade 9.25" X 8" prop, and invest in a tiny tach to measure rpms.

I found good information in this thread regarding pretty much the same issues I've had.

http://forums.iboats.com/forum/gene...449-prop-for-1977-15hp-evinrude-2-cycle/page3

Well it only took 15 months but I finally had a chance to try out some different props. Last year I only went out on the lake once. $80 annual pass made that the most expensive launch fee I hope to ever see!

I ordered two Solas aluminum props. A 4 blade 9.25X8" and a 3 blade 9.25X10". I first ran the boat with the original old beat up 3 blade 9.50"X10". The result were pretty promising. Might just stick with the 4 blade 8 pitch. The hole shot was ridiculous, got me right in the middle of the power band, did not over rev with me solo. All these numbers were with the hydrofoil removed. I'm going to go back out with the fin on and see if it changes anything. It would be interesting to see what the boat would do with me solo and the 10 pitch but I have my kids with me 99.9999% of the time. I really expected that the 3 blade 10" was going to be the ticket and the 4 blade 8" would only see use if I had a second adult.

The old 3 blade 9.25" X 10":
Kids midship in seats - 5050 rpm 13 mph 34.76% slip
Kids on bow - 5120 rpm 15 mph 25.75% slip

Solas 3 blade 9.25" X 10":
Kids midship in seats - 5169 rpm 15 mph 26% slip
Kids in bow - 5220 rpm 16 mph 22% slip

Solas 4 blade 9.25" X 8"
Kids midship in seat - 5620 rpm 15 mph 15% slip
Kids in bow - 5850 rpm 17 mph 8% slip
Me solo - 6170 rpm 19 mph 2.4% slip

Think I might trade back the 9.25"X10" and see if a 9" pitch wouldn't work better? Think my old motor is just a little too tired to spin the standard 10" prop anymore.

So as indicated in the topic the Solas 4 blade 9.25" x 8" would be the best choice? #2113-093-08

http://boatpropellers.iboats.com/Solas-Amita-Propellers/2113-093-08/

 

[ondarvr]

Ordering a prop is a mistake, cancel it if possible. You have no clue as to what prop you will need until after you use the current motor and prop combo on the hull you decide to buy.

 

[jbcurt00]

Yep ^^^ and w out knowing what RPM you're running at WOT w currrent setup, buying a new prop will still be a stab in the dark.

 

[airshot]

If you put a 15hp carb on a 9.9 that was not designed to do that you may be causing your engine to loose power. According to OMC there were certain years and model numbers that could use the carb swap without any other adjustments. I used to own one and was given the spec thru OMC to make the change and it worked very well. However I have heard of many that just swapped the carbs without knowing whether their motor was compatible and if it was not then a performance loss was experienced. If you motor is running properly and weight is balanced properly you should be able to get her up on plane. What are the chances of trying your motor on a friends boat and see what it does??? I am just thinking that your motor is not performing as it should.

 

[Acton]

If you put a 15hp carb on a 9.9 that was not designed to do that you may be causing your engine to loose power. According to OMC there were certain years and model numbers that could use the carb swap without any other adjustments. I used to own one and was given the spec thru OMC to make the change and it worked very well. However I have heard of many that just swapped the carbs without knowing whether their motor was compatible and if it was not then a performance loss was experienced. If you motor is running properly and weight is balanced properly you should be able to get her up on plane. What are the chances of trying your motor on a friends boat and see what it does??? I am just thinking that your motor is not performing as it should.

I actually had that same concern before I made this topic, so I had started another topic regarding the motor itself. I've put well over $1000 (more then the engine was originally worth!) into this engine, including but not limited to completely rebuilding the carb, replacing the head gasket, replacing the fuel pump but none of it seems to make a difference. I've got 93 psi on both cylinders and while some may think that compression isn't that great, I've found that compression in these older outboards is usually a matter of opinion on what's "good" in an older outboard. I'm not ruling out that it's an issue with the motor itself, but after the discussion in the previous topic it was put forth that it was most likely the boat itself that was the issue. Considering all the work I've already put into the motor with no change I have to think that may be the case.

Regarding the carb itself the swap was done by a previous owner, I've read up on this though on leeroys ramblings and what he's posted was that all the cdi ignition 9.9 and 15hp model evinrudes and johnsons after 1975 where identical other then the carb. I've seen it mentioned elsewhere that the exhaust is different on the two engines which does effect horsepower, but I'm not sure if that's really the case or not. In my case I have a '78.

When they designed this series of motors, they designed it as a 15 hp and then detuned it with a different carburetor for the 9.9. When the 9.9hp and 15hp came into being in 1974 and up thru 1978, the only real difference between the two motors was the carburetor. In 1979 they added a shim, part #325038, (one for each cylinder), behind the leaf valves and under the stop plate for the 15 hp, apparently to allow the motor to suck more fuel and air mixture in.
The owners manual indicates that the operating range RPM for the 9.9 to be 4500 - 5500 where for the 15hp it is 5500 - 6500 RPM. So where the 15hp gets it's power over the 9.9 is that the carburetor allows more fuel/air to increase the RPM by 1000 which equal the extra power.

http://www.leeroysramblings.com/Johnson 9.9_15.htm


I think the next step for me is doing a good decarb on the motor which hasn't been done yet, then seeing what the rpms are under load @ wide open throttle with the new boat. I checked the bottom of the hull near the transom on my current boat today and it's definitely rockered. I'll post updates on what my findings are here since I've seen this issue brought up frequently and it's nice to see what the solution was for those following in my footsteps in the future. I think I'm aware of all the variables at this point, so if I rule everything else out it's back to the drawing board with the motor.

 

[Scott Danforth]

At 93 psi, your marginal on compression.

 

[Acton]

At 93 psi, your marginal on compression.

There was discussion about the compression on my motor in my other thread regarding the motor itself and many people are able to get to 20mph+ with similar compression readings on the same setup.

http://forums.iboats.com/forum/engi...78-9-9-evine-slow-wot?p=10172337#post10172337

I saw a page on-line today that said compression on a used 9.9/15 shoud be at least 90psi.
A used motor with 110psi is considered best in class.
They also said electric start will boost that 15psi.
in any case,93 don`t sound that bad.
My 57 model Johnson 3hp twin has 65psi.
Another option is the newer modified flat bottom V hybirds.
I also have a 1236 flat jon.My like new 8HP rude will not plain it off with 2 people&gear.I went to the Solas lower pitch prop,but have not had chance to try it out.
Bottom line,get a boat newer than Noah`s Ark!
Just kidding.

When I first bought the motor I came here to iboats with concerns about the compression and I was reassured that 93psi on both cylinders was fine on such an old motor, and the fact that the compression was equal on both sides was a good sign. Obviously if I rule everything else out then the compression would probably be the issue, but if the compression is the issue then I wont get up to the specified rpms at wide open throttle under load correct? We'll have to wait and see if that's the case as I just purchased a tiny tach today and haven't had a chance to check rpms yet.

 

[airshot]

While I no longer have the information from OMC on the 9.9 that I sold many years ago, if my memory serves me correctly, the carb update from a 9.9 to a 15 hp started in the late 80"s, I believe 86-87, on my paperwork it was not recommended on any thing from the 70's or early 80's. My papers showed until 94 but also included a list of model numbers that it applied to. My 94 model had compression in the 130's, it was considered bad if below 100. Can't say about the year of yours but 93 does sound quite low. I currently have a 1987 as a kicker motor and it has a carb conversion done by a previous owner and it has 120 plus per cylinder, can't say anything about planning with it as it hangs on my 22 ft boat....no getting that on plane there!

 

[Acton]

While I no longer have the information from OMC on the 9.9 that I sold many years ago, if my memory serves me correctly, the carb update from a 9.9 to a 15 hp started in the late 80"s, I believe 86-87, on my paperwork it was not recommended on any thing from the 70's or early 80's. My papers showed until 94 but also included a list of model numbers that it applied to. My 94 model had compression in the 130's, it was considered bad if below 100. Can't say about the year of yours but 93 does sound quite low. I currently have a 1987 as a kicker motor and it has a carb conversion done by a previous owner and it has 120 plus per cylinder, can't say anything about planning with it as it hangs on my 22 ft boat....no getting that on plane there!

I'm not doubting your info but compression numbers and the difference between a 9.9 and 15 seem to be the two most common topics of discussion in most of the threads I've seen here on iboats when issues such as these are discussed. There never seems to be any consensus on what good compression actually is on these older outboards. While you might be right the compression on my motor is something I can't change, and being that I've pretty much put more money into the motor then it's actually worth I'm all in at this point. In my region it's pretty hard to find a decent evinrude below $1000 without taking a gamble, so I decided to stick with the devil I did know instead of taking a gamble on another motor.

Here's some interesting information on youtube concerning the conversion from 9.9 to 15 for the 74-92 models. While I don't trust everything on youtube this video does restate what was already mentioned in leeroys ramblings which many people use as a reliable reference for good information on these motors.

https://www.youtube.com/watch?v=V7rP8oOcAVQ

 

[ondarvr]

Don't be all that concerned about compression numbers, all gauges read differently, some significantly, plus when using a manual pull start you typically get lower numbers. If it idles and starts well then chances are you're just fine.

 

[Watermann]

My bet is the current boat does not have enough beam width to get on top the water, it looks very narrow. Also you might not have a proper understanding of deadrise as it looks to me in the pics your boat is flat from mid ship to the stern. The rounded edge transition from the bottom to the sides isn't deadrise, it's the degree of rise from the center of the hull to the sides.

The current boat I'm working on has a substantial dead rise as seen below.

 

[Scott Danforth]

As for 20+ mph with a 9.9 on a 12 foot boat. Plausible, however doubtful. My guess based on similar boats with 10hp would be 17 to 18mph with one person

 

[airshot]

There have been lots of people that have experimented with various things on motors for many many years and some have found things that work even though the factory does or does not recommend them. I was only giving the information directly from OMC at that time. I have also read material from various books that claim to be factory spec service manuals that differ greatly from one book to another so... who can say for sure. I can only say what worked in my case.