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Little boat big engine and need some ideas

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Little boat big engine and need some ideas

Old 08-05-2007, 11:33 AM
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charlie03
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Default Little boat big engine and need some ideas

i have a home built boat that i made to look like a river jet boat. (north river,alumaweld) it seems to hop out of the water alot when runnning and is fairly unstable. it about 32 inch long, its powered buy a o.s. vrm .65, im runnin a panther 245 prop. and sometime during heavy accel it will vilently tail walk. anybody have any ideas on setup. the hull has a 7 0r 10 degree v, but i can remember.
Old 08-05-2007, 11:49 AM
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Default RE: Little boat big engine and need some ideas

for one... it sounds underpropped unless its a submerged setup? I use to run a 245 on my .45 boat... 250, 255 and X455/3 on my .65 boat.

As for it "tail walking"... do you mean its chine walking (rocking side to side) or its pulling to the right making you put alot of left rudder correction in it?
Old 08-05-2007, 08:01 PM
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charlie03
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Default RE: Little boat big engine and need some ideas

ya i can run a bigger prop but i cant run full power so it dosnt really matter yet. as for tail walking i mean it turns right very hard sometimes like the props pulling the transome to the left. but thats not my big concern. can anyone point me in the right derection to correct my bouning problem. then maybe ill feel better about a bigger prop, unless being under proped is my problem. Thanks
Old 08-05-2007, 09:05 PM
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Jerry Dunlap
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Default RE: Little boat big engine and need some ideas

IMO - way too much power in way too small a boat. Most .65 size hulls are 38 - 40". Also, if it's a flatbottom(and that's what I know most of the full size boats you mentioned are) you have other design issues.

JD
Old 08-05-2007, 10:37 PM
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charlie03
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Default RE: Little boat big engine and need some ideas

thanks jerry, im liking the to much power part. the hull is 7 degrees, semi vee design. do you have clue or what im lookin for to fix the bouncing problem. i does it even at slower speed like around 1/4 throttle. ive tryed adding some weight but im not sure if i had enough on had to fix it if its a weight problem. and ive tryed moving the prop around. its alittle better than its first run. but ive only been able to run it twice since ive built in. any tips on what im lookin for.
Old 08-06-2007, 08:19 AM
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Default RE: Little boat big engine and need some ideas

Try some trim tabs on the stern also some turn fins in center of hull may help the turns.
Old 08-06-2007, 09:27 PM
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charlie03
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Default RE: Little boat big engine and need some ideas

thanks f16man, im going to get some trim tabs for it, where sould the turn fin be located stern, center of boat on keel, or near the bow on the keel?
Old 08-08-2007, 06:56 AM
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Default RE: Little boat big engine and need some ideas

Center of hull on the keel, a 7% v is'nt much so I would think that the turn fins will help keep the boat more stable in the straights and realy help in the turns just like on my full scale rasoncraft, not too much trim tab angle tho cause they will affect your turning performance . When I go into a turn I have to let up on the cavitation plate to let the stern slide around with the rudder deflection. All my squirt boat buddies can't belive a boat can turn as well as mine he he he.
Old 08-08-2007, 07:01 AM
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Default RE: Little boat big engine and need some ideas

Still tho like Jerry said thats a lot or engine for that size boat.
Old 08-08-2007, 08:12 AM
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Default RE: Little boat big engine and need some ideas

post pics,lets see this beastie....and what you've got to work with.....
Old 08-08-2007, 08:37 AM
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Ron Olson
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Default RE: Little boat big engine and need some ideas

Two things come to mind. With the big-block in there plus I'd guess a larger fuel tank the CG is too far forward. The prop might not be sharp giving it the paddlewheel effect. The shallow Vee isn't helping either and you might not have enough rudder in the water.
Old 08-09-2007, 12:29 AM
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charlie03
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Default RE: Little boat big engine and need some ideas

thanks guys for the responses, ill get pics of it on here soon. im still in its testing stages. i made some trim tabs and had a chance to run it today after work in the straight line i got it to run near perfectly all the way up to wide open throttle with very little keel walk. its scary fast. ill be puttin on a bigger prop next run, its also sharpend much better, i do think a better egde on the prop will help, because the transome pulls to the left really hard if you give it to much throttle to fast. ok now the qwestion? since ive got going striaght figured out, will a turn fin on each side keep the backend from trying to pass the front ? my last run for the day it did it at around 50% power, while turning to the left( slighty ) and right when i went wide open throttle. i was feelin trigger happy buy then, and now im missing a left gunnel rail and wind sheild, and will be going some fiber glass reinforcements where needed. ill be making my own turn fins for it. how far should they hang down? and i remember the the hull is only 28inchs and 3 lbs (nothing in it), 10inch wide. what can i say i wanted to build a super fast mono and still be a scale of an everyday boat around where i live. as far as my cg its pretty much right on at around a half tank of fuel.
Old 08-09-2007, 12:31 AM
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charlie03
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Default RE: Little boat big engine and need some ideas

and my prop is hanging down around 3.5 inches. it needs to be sharpened still. lots to do for my next outing
Old 08-09-2007, 12:34 AM
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charlie03
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Default RE: Little boat big engine and need some ideas

i have posted a pic of my 1/8 hydro in my gallery
Old 08-09-2007, 12:48 AM
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charlie03
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Default RE: Little boat big engine and need some ideas

and so you guys know it ran so good in a straight line i dont want to mess that up. i just want it to turn a little better, it doesnt have to turn like a hydro.
Old 08-09-2007, 03:22 AM
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Default RE: Little boat big engine and need some ideas

Here's a pic of what f16man was suggesting


Center of hull on the keel, a 7% v is'nt much so I would think that the turn fins will help keep the boat more stable in the straights and realy help in the turns just like on my full scale rasoncraft, not too much trim tab angle tho cause they will affect your turning performance . When I go into a turn I have to let up on the cavitation plate to let the stern slide around with the rudder deflection. All my squirt boat buddies can't belive a boat can turn as well as mine he he he.
Those fins help my 16' boat turn on a dime. It's scary how fast it will turn. If you wanted to try it out on your boat I'm not really sure how it would be best to do it. You could always try a test one made out of ply. The problem would be a good way to attach it to the boat.

pic was taken this winter while the boat was up on blocks for a new paint job.
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Old 08-09-2007, 07:38 AM
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Default RE: Little boat big engine and need some ideas

Yep thats what I was talkin bout , Iwould make them out of aluminum sheet maybe 1/32 to 1/16 sharpen the leading edge as you would a rudder. make them long enough to bend the top over to attach to the inside of the hull. You will need to cut some slots in the hull to slide them thru and epoxy in place.
Old 08-10-2007, 01:58 AM
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charlie03
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Default RE: Little boat big engine and need some ideas

ive gott many pis posted im my gallery of my toys now. and you can see what im workin with. the pic of the bottom of my mono has small black line on the keel, thats the thats the most my cg will go forward with a full tank of fuel. let me know what you guys think about my first scratch built mono.
Old 08-10-2007, 06:52 PM
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Default RE: Little boat big engine and need some ideas

A prather 245 is 57mm x 89mm pitch, right? Does this prop have a lot of lift? If it does, I'd go with a different prop. May a different prop like an abc 57 x 73 or 57 x 76. You might lose some speed, but gain more stability? Anyone? maybe?
Old 08-10-2007, 09:05 PM
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charlie03
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Default RE: Little boat big engine and need some ideas

sleepy306, those are the figures i have for my 245, i do not no much about the diffrent props out there and this prop and my 250 may have a lot of lift. lease props are what i had for my 1/8 scale hydro that i dont run anymore. (has some minor hull damage from a bouy) as far as proping down i cant, the panther 245 is as small as i can go with my .65, it over revs with the 245 on it. maybe someone on here can give a tip on what props have the least lift, but have the same forward thrust as a panther 250 pr 255. but i do realize that i propblay wont be able to cure all the isuse with my mono because of its engine size.
Old 08-10-2007, 10:14 PM
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Default RE: Little boat big engine and need some ideas

but i do realize that i propblay wont be able to cure all the isuse with my mono because of its engine size.
Hi Charlie,I think you hit the nail on the head with that statement,and not only engine size,but hull configuration also,you've got a great AIRBOAT platform there with the w i d e ,somewhat flat bottom,(and thats probably the only thing keeping it from twisting itself over n over from torque roll)...[:-],but i'm an optimist,so lets try one issue at a time, first, you've got to get that center of gravity at least to 1/3 hull length....from where it looks in the pic it's about 20%,(should be 30ish), short of moving your engine forward,try adding a bottled water to the bow area,just to see if that calms the ride down abit..the extra weight will not be an issue (yet,).make sure your strut angle is zero,just to get a baseline for future adj. and see how it goes.....don't do wide open throttle runs ,try to get the boat STABILIZED first....If you only get 1/2-3/4 throttle,consider yourself lucky,that hulls wide area is trying to like get a barge to plane....do not try to underprop it ,you'll just over-rev(blow) the engine....after re-reading your post,( I had the hull#s wrong with another thread i was looking at) your boat is kinda small for that engine..(LOL) but ,lets deal with it's issues.....a center skegg will help,turn fins will help ALOT more,install at 45 degree angle where the chine meets the hull,I would make them 1" wide at the top, x 2" length, tapered down to about 1/2"wide,keeping the taper towards the rear....as for your trim tabs,bend the starboard inside corner down about 1/8" to offset side-side chine dancin.....good luck buddy....keep it under 100mph....
Old 08-11-2007, 02:32 PM
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charlie03
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Default RE: Little boat big engine and need some ideas

thanks mopartybob, ive got the boat to ride smooth in a strait line and can run it flat out now. it chine dances very little, and when it does a flick of the throttle and it stops doin it. im workin on closing in the bow area and adding fiberglass to the inside to stiffin things up, then im going to build a hard to for it.
Old 08-11-2007, 02:58 PM
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Default RE: Little boat big engine and need some ideas

flat out in a straight line.......post vids of this little beastie....
Old 08-11-2007, 03:56 PM
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charlie03
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Default RE: Little boat big engine and need some ideas

im hoping to post a short video in a week or so. its deffently got some speed
Old 08-11-2007, 04:36 PM
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charlie03
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Default RE: Little boat big engine and need some ideas

pic of little boat

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