Help with an Old School Tunnel

[Robert Elder]

Towards the end of last season, I traded a guy for a Prather Tunnel hull with a KB 3.5cc outboard on it that had never been completed or run. I finished her off and started tinkering with it late last year. All my other boats are FE so this is kind of a novelty for me. I have had some great advice from many folks here and I think I am now within 10% of having it dialed in. I think I can still raise the prop a little but the runs are getting faster.

My question is about handling in the turns. We run and oval with the driver stand towards the north end of the pond.I have no problems turning at full speed there. Once I start to turn, the hull flattens and digs into the turn. The problem is that it doesn't seem to want to turn at the far end of the pond and slides sideways a bit and I find I often have to come off the throttle quite a bit in that turn. Too bad that I am finding that this outboard( and pipe) isn't too happy if I come off the throttle very much.

What suggestions can you make for me?

btw, this is a shot from late last year.

 

[Jim Mamaril]

Towards the end of last season, I traded a guy for a Prather Tunnel hull with a KB 3.5cc outboard on it that had never been completed or run. I finished her off and started tinkering with it late last year. All my other boats are FE so this is kind of a novelty for me. I have had some great advice from many folks here and I think I am now within 10% of having it dialed in. I think I can still raise the prop a little but the runs are getting faster.

My question is about handling in the turns. We run and oval with the driver stand towards the north end of the pond.I have no problems turning at full speed there. Once I start to turn, the hull flattens and digs into the turn. The problem is that it doesn't seem to want to turn at the far end of the pond and slides sideways a bit and I find I often have to come off the throttle quite a bit in that turn. Too bad that I am finding that this outboard( and pipe) isn't too happy if I come off the throttle very much.

What suggestions can you make for me?

btw, this is a shot from late last year.

Lengthen your pipe a little at a time until you can get better throttle response. I ran this same hull many years ago and they are not very user freindly,you have to settle them down going into the corners and then accelerate through. The only other option is to change the bottom of the sponsons. Stumble block placement is also critical on these, if I remember right the right side block was farther back than the left. Hope this helps.

 

[John Knight]

Ah, the Prather 3.5 Lap Cat was my very first boat 20 years ago. It is heavy but tough as nails as it is made of epoxyglass.

Is there a turn fin on the hull bottom of the right side (starboard) about 7-8" from the transom? The boat will not hardly turn without it.

 

[Robert Elder]

Ah, the Prather 3.5 Lap Cat was my very first boat 20 years ago. It is heavy but tough as nails as it is made of epoxyglass.

Is there a turn fin on the hull bottom of the right side (starboard) about 7-8" from the transom? The boat will not hardly turn without it.

Yes there is.

It seems weird to me that I only have issues turning at one end of the pond and only with this boat...

 

[HTV Boats]

Ah, the Prather 3.5 Lap Cat was my very first boat 20 years ago. It is heavy but tough as nails as it is made of epoxyglass.

Is there a turn fin on the hull bottom of the right side (starboard) about 7-8" from the transom? The boat will not hardly turn without it.

Yes there is.

It seems weird to me that I only have issues turning at one end of the pond and only with this boat...

Stand at the other end of the pond and see if it turns better at that end. Untill you have total throttle control it will be hard to run consistently. Running on a regular race course most people hit a much better and closer line in turn one than turn two. Your just closer and lined up with the entrance bouy. Different props may hold the nose uo better through turns. Seems like the X438 and X or M440 were the bread and butter props for those back in the day. Grimracer 40X53/2 is also a good choice on most any .21.

Mic