Props in Props Out - NTB

[TCHB]

My twin engine toon has the props spinning inward. Not sure if anything would change if they were spinning outward. My boat stays under 70MPH so maybe it does not make it a big deal.

 

[Hasselhoff]

Hasselfhoff your backwards on which rpm climbs according to Tres Martin class.

Dave,

My experience is from Tres sitting in my boat, watching my tachs. He is the one that first pointed it out to me. He claimed its one of the primary reasons people spin out their cats. The outside prop starts to aerate and prop slip, raising the RPM and increasing the slip, which increases the RPM, and so on until the prop blows out and the boat looses grip and starts to rotate. Don't take my word for it. Go jump in a cat and get up to speed. Initiate a turn and watch the outside tach climb. Keep turning harder and it will keep climbing while the inside tach doesn't move.

 

[RiverDave]

Hassellhoff my memory isn't the greatest but I could have sworn when I took the class he said the inside RPM's climb because they are being taken out of the tunnel and being more sheltered by the sponson. The outside prop maintains because it is being drive. Into the tunnel where there is clearer water. If the outside prop climbs that's the first indication that you are fucked.

I might have it backwards but that's what I remember anyways.

 

[AzGeo]

Testing twins on a straight keel (non-stepped bottom) V-bottom boat: "turning out" tended to 'carry the nose better and improve speed' at normal trim settings, and "turning in", seemed to 'lift the tail' and improve control, but scrub off top speed per RPM.

 

[djunkie]

This whole fiasco makes me never want a twin engine boat. LOL

 

[Hasselhoff]

I think you might be remembering his explanation of what happens behind a v hull. When a v hull is turning the inside prop is being pulled though the hole the shape of the v creates. This would lead to over rotation on the inside and the outside prop would have cleaner water. The inward lean doesn't cause the outside prop to come out of the water because props are low in the center so not the same risk as with a cat.
If you can imagine looking at a cat from behind while its running with the props rotating right at the surface. Now lean that cat to one side or the other and the outside prop comes out of the water more and more.
What's really scary is how many people I hear saying they drive their cat "around" the turn by giving the outside prop more throttle. Making a bad situation much worse.

 

[Stainless]

This whole fiasco makes me never want a twin engine boat. LOL

It's really not that complicated if you are using "Lucas Prop Rotation Fluid". Takes all the guess work out!


Sent from my iPad using Tapatalk

 

[steamin rice]

In my experience with my boat, a 34' V bottom that runs about 85 MPH, I found the following: Spinning props in resulted in more bow lift and a little bit more top end speed, but low speed handling around the docks isn't as good as with the props spinning out. My boat runs better overall with more bow lift so my props spin inwards. I haven't run into any handling issues at speed, but I tend to be fairly conservative and don't push things on my boat. My understanding is that in general, V bottoms pick up speed with the props turning in, at the expense of handling around the docks and potential handling issues at speed for some boats.

I don't know how this translates to cats or for boats running 100 +, and am following this thread to see what the comments are.

I'd be curious the read comments from Gary Smith regarding prop rotation on big high power cats, as I think he has spent a lot of time playing with different setups on his boats.

 

[VoodooMedMan]

<-----Glad his boat has one engine.

 

[RiverDave]

Dave,

My experience is from Tres sitting in my boat, watching my tachs. He is the one that first pointed it out to me. He claimed its one of the primary reasons people spin out their cats. The outside prop starts to aerate and prop slip, raising the RPM and increasing the slip, which increases the RPM, and so on until the prop blows out and the boat looses grip and starts to rotate. Don't take my word for it. Go jump in a cat and get up to speed. Initiate a turn and watch the outside tach climb. Keep turning harder and it will keep climbing while the inside tach doesn't move.

Ya know I just happened to be on the phone with Tres today.. . And I asked him about this. He said "inside drive gains rpm." He did say in some "rare cases" the outside drive will but for most cats that's the sign of trouble..

Figured I'd let ya know.. Your backwards. If your outside tach is claiming and inside is maintaining you are doing something wrong unless you are one of the "rare cases."

RD

 

[IN AWE]

Top Fuel Hydros spin the props inward for safety and don't even have to worry about the speed.

 

[Hasselhoff]

Next time your out in a cat watch the tachs through the turns. I would be surprised if my boat was the "rare cases" and I doubt it was because I was doing something wrong considering who was with me. But who knows...maybe.

 

[RiverDave]

Next time your out in a cat watch the tachs through the turns. I would be surprised if my boat was the "rare cases" and I doubt it was because I was doing something wrong considering who was with me. But who knows...maybe.

Call him up.. His cell is on his website. I was talking to him about something else and then said "Ya know.... since I got you on the phone."

Inside drive is being sheltered by the sponson usually in the turn which allows for higher slippage.. Outside drive is being pushed into the tunnel (water) which will drive the boat and maintain RPM.

And I have driven plenty of cats, and I do watch the tachs.. I have also taken the class etc..

RD

 

[Tom Brown]

And I have driven plenty of cats, and I do watch the tachs.. I have also taken the class etc..

Sure but have you ever gotten drunk and eaten a cheeseburger off the floor of a cat flying at high speed?

 

[RiverDave]

Sure but have you ever gotten drunk and eaten a cheeseburger off the floor of a cat flying at high speed?

No.. LOL But I have been drunk and passed out on the floor of a Cat at high speed.

RD