My 12' hydro and advice needed for setup.

[Jimmy70]

Wow finally been able to make a post here as I thought something was messed up.

Okay I built this 12' hydro, 7' bow, 21" freeboard, 56" bottom at transom and 72" peak to peak on the transom and with a 15 degree slope. The whole boat is made up of marine plywood with fir and ply interior supports. I have installed floatation from the bow to the back of the seats on both sides, the good pour in stuff. The bottom is 3/8" ply, sides of the sponsons are 1/4" ply and the sheeting is all 1/8" on the top side. I am using a 115hp inline 6 for a engine on this with a 19 SS prop pitch. It sure makes the boat get up and scoot too. I wanted a two seater so designed if for that and could actually install a third behind the two seats. I do not at the present have any turning fins and don't know if I want to install any either as I am not racing, just racing for top end speed. Course I know the engine is heavy at 320lbs and may need to throw some weight forward for more balance but the boat does run very smooth on the water.

My first run out taking it easy and with a little chop I hit 50mph by GPS but didn't want to push it above that because of the wind blowing. My next run out which was on the 3rd of this month I hit 57mph with the GPS but got some bow lift on the starboard sponson as the wind was blowing in on me on the front starboard quarter so I backed down off of that. I still had throttle to go so don't know what it will max out at but I may not want to find out unless it is stable.

So do you guys have any advice to try that I may make the boat run stabler?
I am open for any advice on the subject. Here are some shots of the boat so you can eye it and tell me anything that might be done to help.





Thanks for any feed back on this issue.
Jimmy

[HRTV]

You have a inline six on a 12' boat is that a 115hp ? others might chime in but as far as I'm concerned you have already gone way over the limit for HP so just be safe.

If you want a stabler ride then down grade your motor to something like a 45HP and forget the third seat you are way over powered and run the risk of getting your self hurt real quick!

Sorry to be negative but thats my opinion.

[Jimmy70]

I have a 40hp Mercury I will throw on it later to try it out. I had this one on my 10' hydro but the best I could get out of it was 40mph by GPS and I really think it should do better than that. I may have to try a different prop as it looks like a standard one with the issue of the engine. What ever that is. I guess I should pop it off and take a look at the numbers.

I know I am pushing the limit with that huge engine but believe me the boat runs smooth on the water and no wobbling around either. The 10' boat has given me a couple scares when it starts paddeling around on the front end.
Jimmy

[MN1]

Looks scary to me too.
I don't know why only one side would lift. I have heard of this happening on some of the old Ron Jones drag hydros running into side winds. But they were going over 100 mph.
Also the prop pitch could be bigger (if ya want to go faster).
Looks like the cavitation plate is about 3 or 4 inches above the bottom, which is OK. You could go to a 26 to 28 pitch prop if it was a racing one. This would keep your rpms around 5500 to 6300. Your rpms with the 19 might be high.

One thing you can do is check the boat for twist. Might have to move it off the trailer. Use a level on the bottom at the transom (make it level side to side) then check the same at the bottom of the sponsons (spanning the tunnel), then do the same at the top of the transom. If you set the boat bottom level at the transom all the others should be level too.
If they aren't then this could be why the boat lifts one side.
Mark N

[ricochet112]

"So do you guys have any advice to try that I may make the boat run stabler?"

Make it about 4 feet longer.

[jeff55v]

little boat

Jimmy, You did a great job building the boat. I hope you have a lot of fun with it.
I have to agree with Dan. Too much motor. The boat is too short and too narrow. Please be safe. Please use a tether type kill switch at the least.
You may consider asking these folks for some pointers:

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[MN1]

Now that's Funny!!
Remember to bolt the motor to the transom!!!
Mark

[pops67g]

Torque is the culprit

The combination of a large propeller, buried deep, and a tall motor makes torque a major enemy here. It's a toss-up whether the motor spins the prop or the boat when you get on the gas hard.

[jeff55v]

Now that's Funny!!
Remember to bolt the motor to the transom!!! Mark

A little humor was intended, yes. But I hope I didn't come off sounding like a smarta$$. The boat and motor are somewhat similar. That's the main reason I suggested asking them for pointers.

Cheers

[Jimmy70]

Hi Guys
The cavitation plate is actually about 3/4" above the bottom of the boat as I did take care to keep that in balance while doing some reading on speed boats. Now for the twist thing that is a possiblity that I will check out if I can get it off and on to some sawhorses and level the boat. I know it is a lot of engine for such a small boat but I plan on building a 16' one next year. It is a tunnel king and looks pretty sharp and can have two people in tandum if I make the cockpit right. I also was wondering about the torque factor as when I was hitting around 55mph that is when I goosed it and it hit 57mph and may have torqued up on me, course I got off of that quick too. LOL Makes the old hair stand straight up in the air for a second or two, which is some cases could be to long...believe me I do bolt the engines to the transom as I have seen some incidents of doing the same thing as the movie shows.

One thing I have been thinking about is the little skeg piece that fits on the bottom of the engine, usually a zinc plate for electrolysis, as I have seen a lot of them set at about 12-15 degrees to the starboard to counteract the torque and keep the boat supposedly running true. Mine right now is centered straight but don't want to mess with it if it is going to make the steering harder at higher speeds. Guess a lot of it is trial and error to get things correctly setup. My other question is would it hurt to throw some weight in the bow section?? Would this help counter balance the engine weight enough from the torque effect??

I was hoping for a brave soul to ride with me to see what the effect would be with two people up front as with an extra 150lbs I think it would make a big difference and help hold the right sponson down in the water too. I might find out this coming Sat. if the weather holds up, not looking for a cold splash either.
Jimmy

[Jimmy70]

Hi Jeff, man if it don't have some humor it ain't fun. I enjoy meeting people on forums and I do know we all have some sense of humor and that is the way to go, course there is always a rotten apple to spoil things too.
Jimmy

[mercguy]

Hi Guys
The cavitation plate is actually about 3/4" above the bottom of the boat as I did take care to keep that in balance while doing some reading on speed boats. Now for the twist thing that is a possiblity that I will check out if I can get it off and on to some sawhorses and level the boat. I know it is a lot of engine for such a small boat but I plan on building a 16' one next year. It is a tunnel king and looks pretty sharp and can have two people in tandum if I make the cockpit right. I also was wondering about the torque factor as when I was hitting around 55mph that is when I goosed it and it hit 57mph and may have torqued up on me, course I got off of that quick too. LOL Makes the old hair stand straight up in the air for a second or two, which is some cases could be to long...believe me I do bolt the engines to the transom as I have seen some incidents of doing the same thing as the movie shows.

One thing I have been thinking about is the little skeg piece that fits on the bottom of the engine, usually a zinc plate for electrolysis, as I have seen a lot of them set at about 12-15 degrees to the starboard to counteract the torque and keep the boat supposedly running true. Mine right now is centered straight but don't want to mess with it if it is going to make the steering harder at higher speeds. Guess a lot of it is trial and error to get things correctly setup. My other question is would it hurt to throw some weight in the bow section?? Would this help counter balance the engine weight enough from the torque effect??

I was hoping for a brave soul to ride with me to see what the effect would be with two people up front as with an extra 150lbs I think it would make a big difference and help hold the right sponson down in the water too. I might find out this coming Sat. if the weather holds up, not looking for a cold splash either.
Jimmy

first off, I would say a 19P prop is no where near enough pitch for that boat. I would probably have started around a 23P, if wanting to stay with a basic prop, nothing fancy. If yuo go with an over the hub cleaver and jack the motor up, it might be disasterous, as the motor would be too much for the boat. Second, the trim tab is there to "help" some of the torque feedback to the steering wheel, if the motor (steering) torques to the left (which most do), then you want to move the tab to the left. But, if you jack the motor up high, the tab is barely in the water to be able to do any good. I noticed your steering cable setup...........is it a "no feedback" type steering system? I imagine the boat (steering) will be a handful at speeds above 60MPH. Please make sure you have an "emergency kill switch" and lanyard attached to you at ALL times, along with wearing a GOOD life jacket. A good 90hp V4 OMC might be a better choice (god, did I just say an OMC might be better?? UGH!).......although not as fast as the Merc!

cool boat though. What's up with the step on the top of the sponsons?

[Jimmy70]

Hi Daren
I do have a 23 pitch but haven't tried this one as of yet but I am sure I will get around to it. The step is for stepping into the boat to keep off the skin as it is only 4mm thick and did not want to damage the skin. I was concerned about them but so far on a goosing turn have not seen it dragging any. Most of the places I have launched the boat at you have to step down to get into the boat so I put those in on each side, although now I wish that I had put them up higher next to the cockpit.

When I went to the drag boat races awhile back I questioned a couple of the guys about why they were just using cables and all they said was for better control, nothing good for me to understand why!! I do have a cable unit on my 10' hydro and it works great too but I just thought I would try this rack and pinion to see how it works. Might not have been a good choice but I can also change it out for a few bucks. I do wear a life jacket at all times and I do have a kill lanyard on the little boat but haven't installed one on this one as of yet, but I will get one and install anyway as I would feel more safer with it just in case..and specially if I am for higher end speed. Don't know what it would feel like hitting the water at 60+ but I would think it would not be good for the body at all and reallly don't want to find out either. Hell I am 71 years old thinking I am still 25. Guess it is just the thrill of the ride..YeHaw..
Jimmy

[mercguy]

Hi Daren
I do have a 23 pitch but haven't tried this one as of yet but I am sure I will get around to it. The step is for stepping into the boat to keep off the skin as it is only 4mm thick and did not want to damage the skin. I was concerned about them but so far on a goosing turn have not seen it dragging any. Most of the places I have launched the boat at you have to step down to get into the boat so I put those in on each side, although now I wish that I had put them up higher next to the cockpit.

When I went to the drag boat races awhile back I questioned a couple of the guys about why they were just using cables and all they said was for better control, nothing good for me to understand why!! I do have a cable unit on my 10' hydro and it works great too but I just thought I would try this rack and pinion to see how it works. Might not have been a good choice but I can also change it out for a few bucks. I do wear a life jacket at all times and I do have a kill lanyard on the little boat but haven't installed one on this one as of yet, but I will get one and install anyway as I would feel more safer with it just in case..and specially if I am for higher end speed. Don't know what it would feel like hitting the water at 60+ but I would think it would not be good for the body at all and reallly don't want to find out either. Hell I am 71 years old thinking I am still 25. Guess it is just the thrill of the ride..YeHaw..
Jimmy

you could put cable/pulley steering in your boat and would probably be better, as long as you used good quality cable.

I was thinking the "step area" was exactly the reason you installed them......makes sense.

I think most of us here have "hit the water" at 60+MPH (I know I have more than a few times!).......is is not all that bad, IF you wear the proper safety gear. But, safety is always the key when pushing a boat and motor to "the limit". Definately wire in a kill switch, since those older Merc control boxes never had one installed. Just tap into the salmon colored wire and ground wire in the control box.

wow.......70 and you are still having fun going fast.....that is AWESOME!!!!!! Kepp having fun, as that is all that matters!!

[Jimmy70]

Hi Guys
Hey went to the river this afternoon and lot of power boat guys around so asked some advice from them.
1. The skeg on the bottom is partly broken off, the guys said get it fixed as it can make the boat squirrly on the rear.
2. Get rid of the rack and pinion and get a good cable steering system.
3. Raise the engine so that the center portion of the bulb sticking out is even with the bottom.
4. Conflicting report here, another guy pulls in and said you ought to try and lower the engine so it is riding more on the diffusion plate. Hmm.
5. Get a chopper prop. Yikes more money..

I meet the guys out in the river basin and we yaked a bit and then they said they would keep a eye on me in case I dumped it if I wanted to make a power run. I had installed the 23 pitch on before I got there to try it out and it sure makes the boat scoot too. I made a dash over to the leeward side of the river were it was fairly calm doing 50mph, turned it around and said to myself "well here we go", got it up on plane then punched it and it got up to 62mph real quick and still had some throttle left and I chickened out as I was starting to get into the choppy stuff. When backing down the boat went into one hell of a wobble on the front end. But came out of it okay and a little bit scared for sure. The guy who informed me about raising the engine said that the engine is not stable enough and causing the swing when slowing down and to see if I can make the engine hard so that it will not swing. Learning somethings I do believe..
Jimmy