My New Boat and need some help.

Hi All
I built this boat this summer and have made some pretty good runs in it but so far have not been able to achieve a full bore run. I got it up to 57mph by GPS and then it lifted somewhat on the starboard sponson and done a little dance for me until I could back it down.

The boat is 12' long x a 7' bow, 21" freeboard, 56" on the bottom portion of the transom and 72" from peak to peak on the transom. The transom is 1 1/2" marine ply with a .050 SS cap with a 115hp inline 6 Mercury hanging there.
I have no skeg or turning fins installed on the boat, I have floatation poured in on both sides from the bow to just rear of the seats.

I have made several runs at 50mph in 6-8" choppy water without to much handling problem but didn't want to push my luck on that either. So far I have not had good luck catching real flat water and to be able to punch it full throttle to see what the max is. Maybe I don't even want to know.

So here are some snaps and maybe you can throw some hints or good advise to do or not to do.
Jimmy

 

Well actually you don't want flat water. you want a little bit of ripples on the water to help break the surface resistance but as little wind as possible. Up here in Hydroplane country (Seattle) there are hundreds of those things around. What you are experiencing is Kiting. That thing is just an airplane wing flying low and the angle of attack is extremely important to getting it to go fast and stay on the water. Fiddle with the trim angle of the engine. It may need to be trimmed in (at the prop) to keep the bow from rising to much. You may also need to try out different props. If you look at the big hydros that hit close to 200 mph they all have front wings that adjust the angle of attack and rear spoilers to keep the bow down.

 

Ike said it pretty well. Optimizing trim is the key to getting the most out of your pocket rocket.

 

OK crasyass jimmy,,,,glad its not a two seater,,,,,,homey starts crying for moma at 50 knots,,,,but really neat looking boat ,,we have the hydrabowl here in dayton ohio ,,,,if you come up give me a call...longliner

 

As I belong to the Glen L forum and we got together for a wooden boat meeting in Guntersville, Alabama the end of Oct. Wow it was cold there in the mornings and wind was blowing and it was really choppy on the lake. I could only get up to 30mph as it was beating the hell out of us. One of the Canadian fellows took a ride with me and we enjoyed a spin around the lake with low speeds. As this lake is huge I was hoping for some fair weather and no wind so I could crank it up but no luck.

Anyway the motor is bottomed out far as it will go for right now unless I can do some shimming or remove the hyd. cylinders from the engine lift to drop it down some more, I just will have to eyeball it a good one and see if I can do anything with it. When I was clipping along at 55mph the nose seemed to stay down good and not lifting like my small boat wants to do. I still think that when I goosed it up a good one then it throwed enough torque to lift the right side somewhat and that may have been what scared me off.
Sure makes you pull the throttle quick..lol...
Longliner it is a two seater, I forgot to post the second inside shot. Hehehe..

Come on down and I will give ya a ride.
Jimmy

 

but I dont see a cup holder for my beer,,,and did you custom make those seats too?,,,nice boat man ,longliner

 

Well I was going to make some holders but just never got around to it as I wanted to get the boat to the boat meeting with the Glen L gang, wooden boats, in Guntersville, Alabama.
Yep on the seats, I seen them in another boat design so as I had some 1/4" marine ply left over, I laid the plan out, cut the ply and made some circle cutouts to wrap the ply around with the help of many clamps, water and sunshine they took a pretty good set. I had the bottoms already cut so it was a matter of fitting and gluing those in place with epoxy. I have a ton of black walnut veneer I bought off this guy so I veneered the insides of the seats with that. My biggest mistake on them was I epoxied them but did not let the epoxie setup and cure for a week like suggested so when I varnished them they got a mottled look to them, but I sure as hell wasn't going to strip them down anyway. I have some slip on cushions for some rearend and back comfort from Old Walmart store that worked out just right and cheap.

So today I made a dash over to the river for another trial run with a 23 pitch prop. There was 4 high speed boats, with those 2.5 engines, 19 footers long and when I pulled up you had thought I had brought the beer for them. They all came dashing over to look at it and then gave me some pointers about what I should do to help things out. So they said they would meet me out in the river basin and sure enough they were just sitting there waiting for me. I told them I wanted to do a high speed trial run so would they come over just in case I dumped it a good one. Yep, be glad to. So we motored over to the leeward side of the river from the wind and I jumped it up to 55mph and then turned around a lit the fire in the bucket. Whew, I pushed up to 58 then decided to floor it a good one and the boat jumped right up to 62mph and then I was starting to get into the wind so started slowing down and the damn thing started fish tailing on me and of course the bow is rocking side to side 2' out of the water, so I hauled the throttle all the way back and got out of it okay. Sure scared the heck out of me on that one. But I have some more things to try for trimming and will go back again, hope my luck holds up.
Jimmy

 

Nice boat, looks like fun. Where did you get the plans? If they are current you might get some help with the trim from the designer.

It seems to me that I recall seeing skags on the full size speedsters.

That much power in that small of a boat should give you quite a ride. At those speeds it seems to me you need both hydrodynamic stability, and aerodynamic stability. Because even if you can a good "grip" on the water, at those speeds air currents over (and under!) the hull could send you out of control. It is not enough to simply "hold the nose down" you need to have pitch, roll and yaw stability to keep it under control.

There was a good article on this subject in a back issue of Wooden Boat Magazine by the Australian guy who broke the world speed record in a plywood boat he designed and built in his back yard in 1996 or so. I think I have the issue I can look it up for you if you want.

Study the big boys for ideas on how they do that. Good luck.

 

Hi Petros
Being I had built a 10' boat from plans I had a good idea as to what I wanted to do with the two seater version. So drew up the plans on some 12' construction paper,a full side view of it as I knew I wanted 21" of freeboard and so far I am happy with the boat. My stupidity got the best of me and not thinking to much about the engine moving on me when backing down from a high speed run as that is when I run into trouble. The engine would kick back from the water pressure and then kick the bow high. So I just got me a transom pin and will be able to lock it in place now.
So once I get this taken care of and hope to hit a decent day I will go back to the water and give it another shot.

I did take it out for another run a few days ago and had a couple guys standing by just in case. I changed out the prop to a 23 pitch and that gave it some high end boost. I hit 62mph, by GPS, and still had some throttle left but chickened out as I was worried about the wobble, which was non existant when running, but when I backed down she went into that high front end wobble because of the engine kick back.
Jimmy

 

I have run in a boat like that only once in my life, in Cancun's Nichupté lagoon, around 1987. The boat was owned by a friend of mine, who invited me for a run with him.
I have to recognize I was really frightened, and we only reached 52 mph!

Cheers.

 

Guillermo
It is amazing we can sit in a car doing 100mph not seem as scary but when you get your butt down close to the water doing 50mph it looks like a 100.
It must be something with the brain and the eyes not making connection with scenery, you have water all around you and on a highway much more scenery to take in at the same time. Don't know for sure but I can say it is scary, I know my fear is from the wobble and thinking about dumping it. So hopefully locking down the engine will give me more confedence and make me feel much better.
Jimmy