bouncing on flat water

[Eric Bourlet]

I really would not go adding strakes especially where you show them. What hull is it? Have you seen any one else with that hull make them work? If so work on the issues pointed out here and get the hull working the best it can before you add any strakes. Gregg is right on as well as the others. A boat will porpoise if the bottom is not dead flat (block the sponsons all the way from the transom to the bow), you are at the transition and not running it fast enough, running the prop too deep, having angle in the motor, ect. are all things that can cause a boat to porpoise. I have found that a good back cut 1440 with the blades exactly the same and a satin finish works best on most 3.5 boats. For goodness sakes don't run a polished prop that can cause your problem too. Another good choice if you want to run a stock prop is a 442 as long as you have the air and get the motor up high enough to let the motor buzz. Get those factors right first before you start modifying the hull.

 

[jydracing]

well seeing how the pic of the under side of my hornet was used to show this I will say this If you are having this problem with the hornet or l y n x all that i can say is that the setup instructions were not followed. These two hulls set up porperly will not have this problem. I am not trying to bash any hull that is on the market but before i purchased the hornet molds i ran the xt 460 and they had the same problem with bouncing. if you added weight or neg in the lowerunit the hull would slow and plow in the turns. the problem was in the bottom of the hull the running surface was not flat and the edges were not sharp and were the run serface made the 90 deg turn up to the top of the hull was not square. these three things tell how the hull will run.

The last 4 to 6 in of the running surface needs to be flat If it has a bow towards the water this acts like a pivot point kind of like a seesaw. If it is bowed in towards the hull that the run serface is shortened to almost nothing and will not support the hull. If the rear of the hull between the run surface and top of the hull is bowed out this will suck down the rear of the hull ant pull the nose up and down. If any edge that contacts the water is not sharp but round this acts like a lifting point sharp edges cut through the water a round edge will try to ride on top of the water. well that's all for now see ya Jimmy

 

[Ed.R]

jydracing , I apologize for using a picture of your hull . It is not the hull i have . Mine are all wof built by myself. It was the best picture I had in a hurry . Thanks for all the insite of the bottom of Hulls . My hull did kinda of a drop down sorta thing just at high speed going straight . 2 to 3 times down a straight away . The bottom of the sponson had a SLIGHT and I mean slight cup in them . Up toward the tunnel part of the hull . I recently re-sharpend and squared all running surfaces .

Again I apologize for using your photo .I'm sure there great running hulls.

Ed Ritchie

 

[jydracing]

Hi Ed I have no problem with it being used what so ever. I just want people to know that if they have a hornet and ever have a problem with the performance of it to let me know and it will be figured out.

It is hard to get people to understand how important it is for the bottom of the hull to be true and square. you brought up another interesting thing also about the sides of the tunnel if they are not stright all the way down it will affect the ride of the hull also. We need to rember that we are working with two factores here being water pressure and air pressure. also when sanding the bottom of the hull I do not use sand paper in my hand what ever you are putting the sand paper on needs to be flat. I use a pieace of hard maple block 2 1/2 sq 10 in long that i had planed and machine sanded flat. I also found a product at the local body shop supply I do not recall the name But it comes in a can like car wax and it is a fine powder that you rub on the surface of the car that you are working on and sand off to find the little dents and dings. I used it on the bottom of a hull and was surprised at the results It is a great way to find problems on the bottom of the hull.

There is another thing that has a big part in the ride of a hull. It is how far the engine sets off of the transome. If you can try putting a 1/8 to 1/4 spacer behind the engine mount. If the bounce gets worse try shorting the orignal distance. I have solved a few handling problems with this. Well hope to see you all in charleston Jimmy

 

[moparbarn]

Let me see if I understand these strakes . Picture below are what I'm representing are strakes . Which placement are we talking about here .
Thanks in advance

Ed.R

i have seen them on the inner edge of the sponson, next to the tunnel, most times. but, i have seen them on the outer edge, also. i have also seen a piece of angle, mounted on the inner wall of the tunnel, flush with the bottom of the sponson, extending into the tunnel. not as much a strake, as much as an added ride surface/"pad". the inner edge strake is the most common, and the most effective, imo. represented by the blue line in your pic.

i'm surprised nobody has said anything about this.....the most common strakes i've seen are on the OUTER edge of the sponsons, not inside. posted this working off my faulty memory . when i got home and started looking at hulls, i realized i had posted it incorrectly. my top speed, ts2, and villain all are on the outer edge.

 

[Jimboat]

moparbarn - the notes in moron's post is referencing some of my notes in preparing an article that I wrote for Hot Boat magazine (April 2007 issue) on "Hump Zone/Porpoising". You can get my full article on my website. You might also find my article on "Chine Walk" (Hot Boat magazine Jan 2008 issue) of interest. There might be other articles there of interest.

All of these performance issues and solutions apply equally to any size/power of performance boat. Call if I can help.

 

[moparbarn]

both articles are linked on screamandfly, that's how i found them, and LOTS more good info there, imho B) . thanx for the tip, and sharing your knowledge .

 

[mike the snake]

Mopar, do you know of people running OS that remove the water?

With very restricted water, my OS after a full tank temps 80 degrees at the plug.

both articles are linked on screamandfly, that's how i found them, and LOTS more good info there, imho B) . thanx for the tip, and sharing your knowledge .

 

[moparbarn]

Mopar, do you know of people running OS that remove the water?
With very restricted water, my OS after a full tank temps 80 degrees at the plug.

i only run k&b 3.5's. all with no water. i block the outlet, allowing some water to get into the water jacket, in hopes it would help "even out" any potential hot spots. i have heard that some of the os guys block off the water....... mostly depends on what temps you see. 180 - 220 is a good range, imo. water temps, prop/load, fuel, & mixture all play into this equation. i live in n. va. my pond water temps are fairly cool year 'round. if i see any even 75 degree water, it's hot out. just keep a good eye on head temps, and test, test, test B) .

both articles are linked on screamandfly, that's how i found them, and LOTS more good info there, imho B) . thanx for the tip, and sharing your knowledge .

 

[mike the snake]

Thanks Mopar. I raced offroad for years, my Novarossi engines loved 240 to 260, they Scream at those temps!

My OS outboard is 80 degrees with restricted water. I'm removing the water and try to get some heat into it.

My Top Speed 2 also bounces, I'm going to follow the suggestions here and see if I can get it dialed in for the Grand Prix race in Fremont this month.

Mopar, do you know of people running OS that remove the water?
With very restricted water, my OS after a full tank temps 80 degrees at the plug.

i only run k&b 3.5's. all with no water. i block the outlet, allowing some water to get into the water jacket, in hopes it would help "even out" any potential hot spots. i have heard that some of the os guys block off the water....... mostly depends on what temps you see. 180 - 220 is a good range, imo. water temps, prop/load, fuel, & mixture all play into this equation. i live in n. va. my pond water temps are fairly cool year 'round. if i see any even 75 degree water, it's hot out. just keep a good eye on head temps, and test, test, test B) .

both articles are linked on screamandfly, that's how i found them, and LOTS more good info there, imho B) . thanx for the tip, and sharing your knowledge .

 

[Jerry Wyss]

Hi Mike, I don't have a 21O/B motor that I run water thru at all,, it can be done and still get the ultimate speed

outa them but you would have better luck with a custom mixed fuel. The problem with water going thru there

is that it forces you danger close to a lean setting. This can be overcome by using a superior oil like Klotz with

high nitro and still be able to protect the moving parts at a near lean setting.

I do away with the artificial water cooling altogether and cool'em with fuel. With fuel cooling only, you can richen

the needle to a point where you get that same 80* temp reading, or any temp for that matter. It just makes it

easier (for me) to get that engine, "over the hump", even with a less perfect prop or boat. Even with that, the XM

has a very narrow "entrance" into where it will really hit the button,, refining the prop and boat set-up can be lengthy

to find that narrow window. I have found it on a small variety of hulls but the right prop is really a Big key to getting

it done, along with a bunch a nitro.

For me, I really don't like dickin' with all that anymore, I favor other "piped" engines that leave no doubt where the

power band is, and they only require the same simple prop.

good luck with it,

JW

 

[knbaudio]

well guys i was going to start a post with this topic but i found this one. I have an old parker tunnel hull that has won many races with an air cooled k&b 3.5 the gold head motor highly modified. i pick the boat up fromthe original guy that raced it and saw this boat just fly. i fixed up some of the scratches and gave it a new look i had him check the motor out because it hadn't been run in awhile all it needed was new bearings. it took me a few time to get a handle on it and set the carb up because of the mods he ended up butting his flow meter on it. and i'd would have never gotten it right so many mods to get it flying it's some where in the nieghborhood of 6 turns on the carb. but anyway the first time i had calm water yesterday and almost 70% humidity it leaned out so we had to richen it then it hopped bad on the glass water the lake big enough i wasn't getting my ripple unless i ran next to another boat but then i would pass them and start hopping and slow down. so i took the shims out of the transom set up and also took the wieght off the front did help at all. i dropped the motor and still nothing so i ask the guy that races it all the time and he said hes never seen that but hes never had it so calm either. i figured out that after i turned is when it stuck to the water and started hopping so i started messing with it after the turns and if i turn it left real quick or wiggle it back and forth i could get it up and running with out the hop but it would submarine on the smallest ripple. so it put the shims back in and that was good but it would blow over if i hit someone elses wake. so i put the wieght back on in all i'm back to the old set up he had and just have to lean it out on hot low humid days and richen it on cooler humid days well at least for florida lol. but this boat love the chop and to get it to stop hopping i have to wiggle it coming out of the corner it doesn't run as fast on calm days at least combared to choppy days. so the set up is fine for me i just know to win on calm days run second in his wake then pass him at the finish because it only take about twenty feet to start hopping and slow down. i was going to try to get some answers but after reading most of the post it sound like you would be chasing you tail so if it isn't broken most the time find a way to make it work for you the rest of the time this is the second time all year the pond has been died calm like this we joke we need to send the chase boat out to make wakes for us.