I need some help setting up my 12' Bullet

[Spaceman Spiff]

So this is the vee hull 12' Bullet from the Glen-L catalog of plans. It's built to the plans with the exception of some strengthening of the frames. Hull weight is about 170lbs before rigging. Motor is a 1990 Johnson 48 SPL(185lbs) with a 12x17 prop.

On my first pass I had the battery at the transom and the 3 gallon tank mid ship. It porpoised badly once on plane.
Second pass I moved the battery and gas can in front of the dash frame and put a smallish whale tail on it. Also, I moved the seat 3" forward. Now it planes immediately and the bow stays pegged in place, but it wants to ride on the port chine for some reason. My seat is center mounted and I weigh 270lbs. I was even cheating my weight over to the starboard and it didn't help. That port side just wants to dig in for some reason. The boat is perfectly symmetrical and the motor is straight.

I realize this is a lot of motor and driver weight for this little boat, but what should I look at to fix this port bias? I made an 11' flat bottom(at the stern) boat similar to this with the same basic motor on it and never had any issues like this. It just wouldn't turn for crap so I sold it. Next one is definitely going to be a tunnel hull.

Stephen

[Spaceman Spiff]

I guess I should start by pulling off the whale tail

[Spaceman Spiff]

[largecar91]

Neat little boat. You say the hull is true so I would try motor height and props to see if it corrects the problem. Have you tried putting the gas tank and battery on the right side in the back (if it doesn't make the stern too low in the water)?

[Spaceman Spiff]

Neat little boat. You say the hull is true so I would try motor height and props to see if it corrects the problem. Have you tried putting the gas tank and battery on the right side in the back (if it doesn't make the stern too low in the water)?

I took the whale tail off and moved the gas can to the right side in the bow. It only weighs about 20lbs with 2.5 gallons of gas. That completely solved the listing problem, but went right back to porpoising almost immediately once on plane. Almost as bad as originally. Like all the weight positioning had nearly no effect on it. Probably just too heavy of a motor.

Should I try another whale tail? I think the last one was either bent or misaligned. Or maybe some smart tabs?
Props are not very plentiful for this motor. 12(or 11-3/4)x19 maybe the only other choice. I could try raising the motor a hole or two.

[Spaceman Spiff]

Finally, a modicum of success. I put an SE Sport 300 on it and that cured the list. Onset of porpoising was at about 28mph. Without it, the onset was about 18mph. I added about 50lbs of sand to the bow and pushed the onset to 30mph(5000 rpm with the 12x17). Still a long way to go in terms of ironing it out. I'm not helping top speed any by adding all the resistance. But it's still funner than crap at only 30mph. I definitely need to move up to the 19P prop. Next, I'll try raising the motor up a hole and see how she does.

[Spaceman Spiff]

Raising the motor one hole had no effect.

[Jimboat]

Onset of porpoising was at about 28mph. Without it, the onset was about 18mph.

you're doing the things that should help reduce porpoising. This hull is very low deadrise bottom so quite susceptible to porpoising. changes that cause reduction of trim angle will reduce porpoising. this hull will be sensitive to weight as this will also affect minimum trim angle needed to attain speed.

[Spaceman Spiff]

you're doing the things that should help reduce porpoising. This hull is very low deadrise bottom so quite susceptible to porpoising. changes that cause reduction of trim angle will reduce porpoising. this hull will be sensitive to weight as this will also affect minimum trim angle needed to attain speed.

Thanks Jim. This motor is not very adjustable for trim. It just has three holes and it's already in the lowest setting. Visually, the motor looks slightly tucked. I may look at adding another hole.

What do you think about smart trim tabs?

[Jimboat]

This motor is not very adjustable for trim. It just has three holes and it's already in the lowest setting. Visually, the motor looks slightly tucked. I may look at adding another hole. What do you think about smart trim tabs?

I'm not a fan of trim tabs, as they can create a handling issue when deployed at speed. if you can't set engine angle as desired, you might be able to install a transom shim to get what you need. the weight balance in hull will also determine hull operating trim angle.

[Spaceman Spiff]

Thanks. I like that shim idea.

[Spaceman Spiff]

Thanks Jim. The shim was the secret sauce. I backed off the upper bolts about 1/2" using washers. I got up to 38mph with no bouncing. Waiting on my 19P prop to go faster. It did list to the port a bit at that speed, but I think just putting both seats in it and sitting on the starboard side should solve that.

How do tunnels hold up against porpoising? Better than a Vee I hope. I'm getting close to ordering Bob Dillon's Laker 12 plans.

[Spaceman Spiff]

Well, I gave up on the 48 SPL on this boat. I'm saving that for my Bob Dillon Laker SC12 which is about 40% complete. I put a 1976 Evinrude 35hp on the Bullet and it was still porpoising pretty good on the second hole from the bottom. That's with the fuel and battery and a 25lb sand bag in the bow. So I went to the bottom hole and that cleaned it up and it behaves nicely at 30mph.

Yes, this is one of the many problems one runs into with obesity. The bare hull weighs about 170lbs and I weigh 100 more than that. I wonder what it would do with a human-sized pilot. LOL

[Spaceman Spiff]

I put a 5" jack plate on there with the 35hp Evinrude and just went nuts with the porpoising. Like as soon as I got on plane, even on the bottom trim hole. So off that goes and I'm going to go back to the 48SPL and work out the kinks on that one.

Stephen

[Mark Poole ModVP]

I know the mentality with Scream and Flyers is always more motor more speed. The problem comes when you put too heavy a motor on a boat that does not have enough bottom. That short little boat with a long shaft 48 is unbalanced and the bouncing problem is because the hull is not long enough. This is a pic of a boat I used to have. It was a copy of a Kennedy Craft. It was 15 ft. long and probably weighed 250lbs. With a jackplate and a stock 30 Johnson with an SST prop it topped out at 38 mph rock solid with level trim. If I would have modded the engine and put a teenager in it I am sure it would have run well over 40. Less engine, a longer hull and the right set up can result in more enjoyable ride.