Top Heavy Tunnel Hull ? -Video-

[home made tunnel]

I'm just talking about making a 3/16 high 1 inch wide strip of Bondo at the end of the running surface / sponson. easy to sand off or lower if too much.

Allison's use a low lip

Well, I do have Gelcoat bottom, I suppose I could slap on some bondo.

Next steps to try -
1) I already Removed through hub 23p cleaver, installed 24p Over hub cleaver, 15" rather than 14.5". It also has much wider blades.
2) Try a slight left turn before it starts to porpoise, and see if I can accelerate through it.
3) Add a sandbag or two up front for weight
4) Raise the motor a little higher (getting close to needing a low water pickup / bobs nose cone)

[home made tunnel]

I'm just talking about making a 3/16 high 1 inch wide strip of Bondo at the end of the running surface / sponson. easy to sand off or lower if too much.

Allison's use a low lip

I'm assuming 1" wide, port to starboard? Not 1" wide bow to stern, that would do next to nothing I'd assume lol.
Next step - IF I put a little wedge on the back, should I put it in the middle of the tunnel, at the orange arrow? Or just bottom of the pads, at the red arrow? Or on the sides also, like the green arrow?

[JPEROG]

Back edge of the running surface.

Joe

[CUDA]

Red arrow, use masking tape make a wedge area , about 1" or 3/4" wide wedge strip on the flat bottom pad,

Or a strake at the top of angled running surface right along vertical side, Good luck Dad

Dreamer

[RUM RUNNER 305]

I would start with the sand bags up front before anything else.

[home made tunnel]

So I went out yesterday and played.
Really getting disappointed with this motor. It should be able to push this 500lb hull WAY better than it is.

I'm loosing faith in the power of this 115 Pro XS. Rev limit is 6300, but if feels like it has no power gains over 4500rpm.
My 120hp Force on the baby-shark redboat blows this thing out of the water.

Results: Keep in mind, these speeds are indicated from the paddle wheel, which reads about 10% low. (40mph indicated = 45gps)

23p 14.5" through-hub cleaver.
No sand bags in bow.
Semi-difficult to get on plane.
Porpoise TERRIBLE above 50mph.
Top speed - 63mph - Violent porpoising. That is not a sustained speed - just a blip
RPM - Just above 6k rpm. (hard to tell as it porpoised so bad.

24p 15" over-hub cleaver.
No sand bags in bow.
Almost impossible to get on plane.
Porpoise still Terrible - at about 45+mph
Top Speed - 52mph indicated
RPM - Just above 5000rpm

Added 100lbs of SANDBAGS under the bow.
24p 15" over-hup cleaver.
On plane in 3 seconds WAY BETTER!!!
Porpoise starting to go away - doesn't come on until 55mph, motor runs out of grunt at 5200rpm
Straight - it porpoising pretty bad that I have to slow down. Slightly turning left, it's ok, but scrubs speed.
Top Speed - 55mph indicated
RPM - 5200/5300 (6300 is tached for this motor).

The motor is already a couple inches above the pads... I could go higher, but it will definitely be harder to get on plane. I'm almost ready to swap motors on my 2 boats haha.

I think I should try some bondo wedges @ the trailing edge of the pads next. Also, wondering about the tunnel skirts - I wonder if that would help any.

It's pretty sad a 115hp motor cant get past 60mph on a 500lb hull. This motor just can't push past it.

[Davidlake]

I am no expert on those motors, but seems that a 14.5 or 15" prop is too big. I run 14.75" on my 300XS's.

[Robby321]

I am no expert on those motors, but seems that a 14.5 or 15" prop is too big. I run 14.75" on my 300XS's.

Kinda agreeing here. Try something in the 12's if ya can find one right pitch.........

[Captaincj]

When the porpoise starts and/or gets worse does it feel like the prop loses bite?

Maybe try lowering the engine an inch or two with the sandbags?

The lower pitch, the higher pitch definitely sounds like it's way too much prop.

[SS Minnow]

OMC v-4 140 hp and my props are 13.5" 3 blade and 13.75" 4 blade. They did have one year where they had a lower that used the v-6 props which are 14.25" and 14.5". There may be more sizes out there, I do not know it all. And, I am running a 2 stroke so not sure if that makes a difference as far as low end torque v prop size.

[home made tunnel]

I am no expert on those motors, but seems that a 14.5 or 15" prop is too big. I run 14.75" on my 300XS's.

Hmm - Maybe - I didn't think diameter had much to do with with it at all. It was a great price on the 24p 15" prop - so I got it. Very hard to find smaller diameter cleavers - but I suppose I could find a prop shop to cut it down maybe.

Kinda agreeing here. Try something in the 12's if ya can find one right pitch.........

Lol - Like I said to David - where do you find small cleavers like that?

When the porpoise starts and/or gets worse does it feel like the prop loses bite?

Maybe try lowering the engine an inch or two with the sandbags?

The lower pitch, the higher pitch definitely sounds like it's way too much prop.

It doesn't lose bite at all. No cavitation issues at all. If I remember a month ago or so - having the motor lower, the porpoising was worse. it started to get better as I raised the motor... Not sure if that's the answer, but I'm all for listening to experience... why do you suggest going lower with the motor?

OMC v-4 140 hp and my props are 13.5" 3 blade and 13.75" 4 blade. They did have one year where they had a lower that used the v-6 props which are 14.25" and 14.5". There may be more sizes out there, I do not know it all. And, I am running a 2 stroke so not sure if that makes a difference as far as low end torque v prop size.

It's really not a low end issue I'm having - it's like the motor just doesn't get any more powerful after 4500rpm.


I have several videos I took from that day i'll upload later tonight.

[Captaincj]

Didn't know you were running it lower. If higher has been better, try a little higher yet I guess, with the lower pitch and the added weight.

[SS Minnow]

.................................

It's really not a low end issue I'm having - it's like the motor just doesn't get any more powerful after 4500rpm.


I have several videos I took from that day i'll upload later tonight.

I meant that you might be able to use bigger props because you have more lower end torque where the 2 strokes do not. I really do not know for sure, that's why I read stuff that you and a few others post, almost religiously.

As far as not making any more power after 4500, do you know where the hp peaks on that motor? Might be a bot lower then where the limiter is set.

[home made tunnel]

I meant that you might be able to use bigger props because you have more lower end torque where the 2 strokes do not. I really do not know for sure, that's why I read stuff that you and a few others post, almost religiously.

As far as not making any more power after 4500, do you know where the hp peaks on that motor? Might be a bot lower then where the limiter is set.

Being a 4 stroke, it probably is lower. Outboards are made torquey compared to day, a streetbike motor that revs to 12k rpm.

I may throw the other prop back on with the weight and try that next.

[Whaaaaat]

Nose cone, and raise prop. If you still have no cone. And are able to keep water pressure your still to low.
Especially with a big diameter wheel. I think the case and prop are adding to much lift at speed. Need to get the bullet up clear of the waters surface

Before going the bondo route. What about some manual tabs at the end of sponsons. Adds the slight hook you may need. And effectively lengthens hull.