Nosecone shape modifications for more stern lift

[Mr. Demeanor]

My boat like transom lift! Right now I am running my gearcase VERY high. Really nothing but skeg in the water at speeds above about 50mph.
I run a transom mounted cooling water pickup so I can go as high as I want without concern for water pressure.
I have run my lower unit both with and without the nosecone and it was about 4mph slower without the nosecone even though the bullet is above the waters surface. I attribute this to the transom lift the nosecone is giving me. I am running on the bottom of the bullet like its a trim tab holding up the stern of the boat. The larger (longer) the gearcase, the more lift and the faster if runs.
I am thinking about grinding a small flat "pad" on the bottom of the nosecone directly in front of the skeg. It would start very narrow at the tip of the nosecone and get wider running back to the skeg where it would blend in. This should get the gearcase up on top of the water sooner.
Has anyone done anything like this or any other modifications to the shape of the gearcase to increase lift?

Heres some video I took awhile back. The first is without the nosecone and the second is with the nosecone. Same engine height. You can see it struggles to get up on top without the nosecone and there is a lot more spray/turbulence.


http://www.youtube.com/watch?v=f6Kl7pB_DZ8&feature=related


http://www.youtube.com/watch?v=WIXvi33I0o8&feature=mfu_in_order&list=UL

[specboatops]

No pro at this by any stretch, I'm thinking that flat area your thinking of adding will actually slow you down, what about lengthening the cone, having the boat ride more towards the back of it ? just a thought. Keep us posted, I as well as others have monitored your success with this little rocket !

[Mr. Demeanor]

Im thinking the "pad" wont effect my top speed as it will be out of the water at wide open but will help me get up on top quicker. You can see in the first video how it struggles to get up on top.

The other thing I am thinking about trying is extending the trailing edge of the gearcase with a ring of some sort. I could extend it 1/2" or by adding another thrust washer, 1" which would be a big increase.

On a side note, she ran the fastest top speed with my 26 ET copy yesterday at 76mph. Conditions were perfect for the bat. cooler air,tail wind and a very light chop. I wish I would have had the 30 cleaver. I think it would have gone 85ish

And thanks for following. I owe a lot to people here who have given good advise and direction and really enjoy tweaking the setup. I have some friends trying to get me to hang a 200 Merc on it but I really enjoy doing something a little different. Its the the fastest stock 4 cylinder pleasure boat I can find any info on so far.

[specboatops]

...I agree, stick with what you're running and continue to think "OUTSIDE" the box.........

[steve@scp]

idk... but, that's the kewlist video i've seen in a long time.
pretty kewl to see how the nose cone rides above the water!!!!!!!!!!!

[Mr. Demeanor]

idk... but, that's the kewlist video i've seen in a long time.
pretty kewl to see how the nose cone rides above the water!!!!!!!!!!!


If you look closely at the first video you can see the water coming off the front of the anti-ventilation plate by the lower unit mounting bolts is actually spraying forward. In certain condition that water actually flows up the front of the midsection and hits me in the back of the head (which isnt too far away :) )
Its not coming up inside the jackplate like some do, its coming up the midsection in the low pressure zone behind the transom and I assume theres low pressure behind my head at 70-80mph as well.

[steve@scp]

lol. i hear ya.


btw.. do you have a holeshot plate on the bottom of the jackplate? that would do more good than griding on the case. (which would scare me)
i'm gonna make my own pretty soon, with a little more (and longer) turn down than most for a quicker holeshot. just a thought.

[baja200merk]

I love how its different, I like being different also :D

I cant wait until you find a project powerhead to port over the winter and shoot for high 90s :thumbsup:

[Mr. Demeanor]

lol. i hear ya.


btw.. do you have a holeshot plate on the bottom of the jackplate? that would do more good than griding on the case. (which would scare me)
i'm gonna make my own pretty soon, with a little more (and longer) turn down than most for a quicker holeshot. just a thought.


I just built a knockoff of an Allison plate for my little Yamaha lower. Thinking about a tunnel tab experiment at some point.

[mr_velocity]

I just built a knockoff of an Allison plate for my little Yamaha lower. Thinking about a tunnel tab experiment at some point.

Did a tunnel extension on our 13' funcat. With the boat being so short took some time to get the extension just right. Had to notch it for the jackplate.

http://img379.imageshack.us/img379/883/p1011423zt1.jpg

[rkmirage]

Which one of your crazy friends said to put a 200 Merc on it? Oh yeah, it was me. Honestly, that 82+ you got was very impressive for a 13ft boat, Put the cone back on it and get rid of the pool cleaner hose! You need to have someone else drive it while you watch how it looks running wfo, its really more impressive to see it than feel it.

[200VEGAS]

nice video,s

[Mr. Demeanor]

Which one of your crazy friends said to put a 200 Merc on it? Oh yeah, it was me. Honestly, that 82+ you got was very impressive for a 13ft boat, Put the cone back on it and get rid of the pool cleaner hose! You need to have someone else drive it while you watch how it looks running wfo, its really more impressive to see it than feel it.

It has a cone on it. I think theres a good number coming. I can feel it. She was running real good on Sunday and that was fresh water.
Scott is the one pushing the 200 idea but this Yamaha just runs and runs and runs.... :)

Pretty sure it looks like this ;)

http://www.youtube.com/watch?v=yMF31PI111s

[rkmirage]

Yep, thats what it looks like.

[Mr. Demeanor]

Not sure if this will show up but I put a small "pad" on the bottom of the cone where the water intakes used to be. Should have taken the pic before I repainted it. This should get me up on top quicker. It will be out of the water over about 75mph so it wont effect my top speed. I will take some video for comparison soon.
Sorry about the pic. Should have wiped the dust off. It runs further back toward the skeg than the pic shows.
246485

[whipper]

I like the padded gear case idea I have something similar I did to mine. Another way to get some stern lift would be to add a foil to the hull on each side like the Allisons have. You wouldn't need much. In your video calculate your correct angle of attach. Add airfoils to side of Hull aft to create more lift. Simple and effective. Your hull looks smooth on the sides. There is zero aerodynamic effect. Your lift is created buy the underside components only. Add some side "wings" for that little extra lift at higher speeds. You could also get technical and determine at what speed based on the hull weight and velocity to calculate what sized wings would add how much lift. The shape and placement will determine the change in angle and lifted area.


You can research Airfoils and find very usefully information as to shape and coefficienties. Most people never notice but look at the shape of the foils or wings on the side aft portion of any newer Allison. The entire shape of the hull could be taken for a big airfoil. More so on the RR but even on the GS the wings are shaped like an airfoil for good reason. Hears a usefull link showing the forces at work and were pressure faces of the air passing by have a possitive effect on lift. The top diagram would be a shape I would think your hull would bennaft from in the stern area. The angle required for lift seems close to the angle of your hull at 82mph. With this shape aft on each side of your hull will get a little natural help in the lift department coupled with the Tunnels effect that accually forces down your stern would aid in lessening the drag that creates. The length and depth you would require to achive this would require some guess work and experamentation. The wing cord would be your rubrail location. http://www.aviation-history.com/theory/airfoil.htm http://i63.photobucket.com/albums/h151/whipperr/DSCF0040.jpg

[Mr. Demeanor]

Little pad worked great and I even ran my best top speed ever. I dont think it had anything to do with the speed but it didnt hurt anything!

[baja200merk]

We gotta get you up here to tarpon, I think I want to see it run with the 34 more then you do! http://www.freesmileys.org/smileys/smiley-laughing013.gif (http://www.freesmileys.org/smileys.php)

Ill tow you up on plane if I have to :D

[Mr. Demeanor]

A little update:

I cant believe it was over a year ago that I ran the best speed with the little pad. Recently I made the pad a little bigger and extended it back further (not being able to leave well enough alone). Well, the handling went to ****! Way too much lift and the boat got very loose. On deceleration, it would hop horribly so much I only made one high speed run for fear of getting wet this year at the Suwannee.
I have filled the pad back in and will test some more.

[transomstand]

Try making the cone a bit wider, more like a tear drop shape, or an old round bottom boat, rather than a "sharpened pencil" look.

[Mr. Demeanor]

Try making the cone a bit wider, more like a tear drop shape, or an old round bottom boat, rather than a "sharpened pencil" look.

I have thought about trying something like that in the past and might do it. I was thinking of taking something like a golf ball, drilling a large hole in it, and epoxying it to the tip of the bullet. Then I would fill in and blend it into the case. I have often wondered why nosecones are pointed when everything else that moves through water at high or even low speeds is rounded. Look at the shape of submarines, torpedoes, etc.

[1FASTLASER]

Thinking out loud...what if the " shape of the cone".... not the length was changed to more of a triangle....starting at the point and keeping the point....the flat on the top side and the tapers onthe sides blending back to the skeg

[Mr. Demeanor]

Thinking out loud...what if the " shape of the cone".... not the length was changed to more of a triangle....starting at the point and keeping the point....the flat on the top side and the tapers onthe sides blending back to the skeg

Problem is water tends to break free from sharp edges and flat surfaces. That is why cones are cone shaped with sharp breaks/edges at the trailing edge of the cone and skeg.
While it might sound good, it might also mean blowout or increase your prop slip if the water is breaking away from the lower unit near the front of the bullet.

[200valeroyt]

Chris, have you ever considered trying some sort of tunnel extension like above post? I'm sure you have, just wondering if it would give more overall lift and speed? Possibly a bit more safe from blow over also? Not sure?

[1FASTLASER]

Mr D.....you right and I know that.....talk about having a cough cough....senior moment

[jpf091959]

Try a cleaver. It should give you some transom lift.