Can't launch with big prop

[anthony_marquart]

I'm testing my new .12 rigger and it's going very well. One problem I'm having is that I can't get the boat to launch with the v937prop. I know this is the prop, or one like it, that I need to run to get to my target speed of 60mph.

What can I do to get this to launch? I only tried twice cause I was having a little engine trouble at the same time. What can I do to improve the "launchability" of this boat with high pitch props? Once on plane I know the engine can turn it.

A different technique? high rpm launch? low rpm? fast toss????? what to do?

The boat is running very well so far. Much more stable than my other .12's especially at speed.

 

[Jerry Dunlap]

"Back in the day" before outboard engines, I was pretty good at tossing DragN'Fli hydros up on plane at launch. It still takes a flat, fast launch to get some Sport 20s on plane off the beach.

Low and hard. Sounds like a good pitch in baseball.

JD

 

[Dan_Cousin]

does the engine bog down or just blow bubbles in the water?

if it bogs down you might try raising the strut a little to allow the rear sponsons to help it get up.

Lengthening the pipe some may work too to get you more low end torque.

Hows your compression ratio? increase that if you can by taking out a shim (make sure the piston doesn't slapt the head aferwards).

 

[Jay Boyd]

Try the famous Andy Brown launch. Dip the tail of the rigger in to load it up,build up heat,be one with the motor & give it a quick shove off while loaded. I could turn a ABC S-15 on my geared OS .11(from Japan) by doing the Andy Brown launch.

 

[anthony_marquart]

It revs pretty well put blows tons o'bubbles. I think I would have to be IN the water to do that Andy Brown launch. Compression is good I think. I can barely keep plugs in the thing. The manual said the engine should run at about 1.75 turns out for break in and a little leaner for final tuning. If I go any leaner than 1.75 it smokes the plug EVERY time. These little engines really are plug sensitive when we run them the way we do in boats. I've seen plugs last months in cars... I'll through a couple in a day running the same engine in a boat.

Still looking for suggestions. Is there a design trait in the hull design that I should be thinking about on this?

Other than this I'm reall happy with the design. MUCH better than my other 12 riggers so far.

 

[Eric Canto]

Anthony, you mentioned that this boat is much more stable than some others you have been running. This could be because you have a lower angle of attack in the front sponsons. This will make the boat more stable but harder to launch.

Eric Canto

The Speed Shop

 

[Jay Boyd]

I forgot,you have to be in the water! It's very cool seeing Andy launch big pitch props this way. Not sure if he still does it,it's been a while.

 

[GMCSW7]

It revs pretty well put blows tons o'bubbles. I think I would have to be IN the water to do that Andy Brown launch. Compression is good I think. I can barely keep plugs in the thing. The manual said the engine should run at about 1.75 turns out for break in and a little leaner for final tuning. If I go any leaner than 1.75 it smokes the plug EVERY time. These little engines really are plug sensitive when we run them the way we do in boats. I've seen plugs last months in cars... I'll through a couple in a day running the same engine in a boat.

Still looking for suggestions. Is there a design trait in the hull design that I should be thinking about on this?

Other than this I'm reall happy with the design. MUCH better than my other 12 riggers so far.

If your dropping if from the shore and not getting wet your going to have problems getting it on plane with a big prop.

Knee deep and launch it flat and fast!! Indiana+November+cold water= burrrrrrrr

Get wet and launch it!!!!!

Steve :

 

[anthony_marquart]

Well,... I HIGHLY doubt I'll be in the water any time soon. I think I'm going to start launching it like a bowling ball!!!! I may go bowl a few frames to get in practice.

I have to keep from falling in....

 

[nitro_nemesis]

Hey tony, remember when I was using a different prop about every 10 minutes one day w/ the rigger you gave me including the v937, never had a moments hesitation w/ any of the props until I tried to use that big 220 and it bogged and choked itself like no other - but remember you said the AOA on those sponsons was lik 5ish - I know your boat ended up being somewhat faster and a little of that was contributed to the difference in motor, but maybe the angle has a little more to due w/ this problem, I can't recall a time I threw that lil' firefighter in the water and it didn't want to jump right back out no matter what the strut height was !!!!! And your new design is lighter than the ff .12 isn't it ??? - or not ... :unsure:

 

[John Finch]

Is it a scratch built rigger, or a kit. There are a lot of things you can do to help the launch if the boat is not a proven design.

 

[PHM Racing]

John were all ear's , i now i'd like to here what you have to say on this B)

 

[anthony_marquart]

It's a bit of both. It's a new design that's a compilation of my experience and advice from this forum.

Yes Mark, this hull is much lighter than my FF. It's also bigger. I need to get back out there and give it a try. I know your FF well. Remember it used to be mine When I was trying to launch this prop I was also having a little motor issue that has since been resolved.

I'm going to try a little longer pipe length and some better, stronger launches.

This boat is much different than a FF. I know this isn't an uncommon problem.

We're still all ears Mr Finch.

 

[John Finch]

Not seeing the boat I am a bit in the dark, but here are a few things. A center shoe or riding pad like Andy's boats will ventilate the prop if you are trying to launch a large prop. Not to be confused with cavitation, ventilation simply unloads the prop because of a protuberance in front of the prop ( the shoe).

Also. wider sponsons get the boat up on plane faster and with less drag from the hull, if perhaps you have narrow sponsons. Also, if the front sponsons are not exactly where they were on a previous boat as far as their position at the trailing edge of the riding surface to the CG, this will change the launch characteristics too. If they are more rearward, they probably need to be a bit wider to lift the boat out of the water as more weight is distributed on them and they could be digging. The angle of attack of the sponsons is equally as important. Too much negative and the boat won't launch. The prop too deep in the water is a possibility and the tub too close to the water is another. ETC ETC. Have you made any of those slight changes to a previous well running model of like design? If so, it only takes a small change to mess up the whole package. The easiest fix I can think of right now, not knowing the boat, is to lengthen the tuned pipe.

 

[Ron Olson]

Tony, give John a link to your Gallery as that should help him a lot.

Don't give your boat any hook shots when launching! :lol:

 

[anthony_marquart]

Tony, give John a link to your Gallery as that should help him a lot.

Don't give your boat any hook shots when launching! :lol:

I actually emailed him the drawings. I'm eagerly anticipating a response!!!!

No,.. I bowl the straight ball,.. right down the middle...

I think I can get it to launch with the right throw... It does have a lower AOA than the other sponsons I've run. The angles on my boat are lower than the angles on the FF but more than the angles Marty reccomends in his setup notes. My FF even didn't like launching the v937. Marks would launch it but couldn't get the prop to hook up long enough to make any speed. I'm confident this boat will keep the prop in the water if I can get off the beach. I'm having a sponson fit / turn fin alignment problem at the moment. I've got some parts on order to correct the problem. It's causing me to have to run a good bit of left rudder to stay straight. I have to think the alignment issue is washing off a TON of speed. The boat is kind of fighting itself. It's running as fast as my FF even with that problem. Ill get that staightened out and the launch thing fixed and then I think I'll have interesting things to talk about!