Turn Fin Placement?

[BneHead]

Hey Guys,

I was wondering where I should be placing my turn fin on my hydro?

I've included a pic. Should I have it at place #1 or place #2?

Thanks all

 

[nitrotoys]

I would say at number 2 to mount, and make mount flush with bottom and angle the fin right under sponson and have the tip end up where 1 is. Thats what i have seen, Just looked at pics of a hydro and thats what it is like.

Tom

 

[gil sonsino]

Number two using a bent fin!

Gill

 

[Preston_Hall]

I would say where "0" would be, flush with the inside of the sponson. The inside edge of the sponson should be sharp because it also acts as a turn fin. If the two "fins" aren't in-line then they will fight each other.

Maybe Donald will chime in on this one since he has built many scales.

 

[Grimracer]

I would say where "0" would be, flush with the inside of the sponson. The inside edge of the sponson should be sharp because it also acts as a turn fin. If the two "fins" aren't in-line then they will fight each other.
Maybe Donald will chime in on this one since he has built many scales.

In thinking...

We run our ride pads on the Ninja sprint and almost all our hydros at 0 on the right sponson (dont know if this constitutes a turning surface and if so not much).. sharp is good.. now if we follow your thoughts (they darn well could be best) then the TF would run toed in if the sponson was toed.

Also in thinking it seem that you would have the most leverage if mounted furthest out.

Bottom line... i think i might mount it outbound as far as you can as this would provide you with the most leverage and the least chance of water coming off the fin and lifting on the hull.

Im still open to more thinking on this one.

Grim

 

[garrett randall]

I think we all need to know what type of hull we are discussing...is it a hydro (rigger) or a sport boat, or doesn't it matter? Does the fin placement act the same on a sport and a hydro?

Never running a sport (scale) boat, I don't know...

Garrett

 

[Preston_Hall]

I would say where "0" would be, flush with the inside of the sponson. The inside edge of the sponson should be sharp because it also acts as a turn fin. If the two "fins" aren't in-line then they will fight each other.
Maybe Donald will chime in on this one since he has built many scales.

In thinking...

We run our ride pads on the Ninja sprint and almost all our hydros at 0 on the right sponson (dont know if this constitutes a turning surface and if so not much).. sharp is good.. now if we follow your thoughts (they darn well could be best) then the TF would run toed in if the sponson was toed.

Also in thinking it seem that you would have the most leverage if mounted furthest out.

Bottom line... i think i might mount it outbound as far as you can as this would provide you with the most leverage and the least chance of water coming off the fin and lifting on the hull.

Im still open to more thinking on this one.

Grim

Grim,

Yes the TF would be toed as well. Not ideal but I can't say I have ever seen a change in speed due to it. Handling characteristics are a different story since this could possibly try to "bind" the boat. A lot of people probably don't know it, but their boats track straight because of this toe in on the TF. And yes, this isn't the way to correct tracking problems.

I agree also that the best leverage would be closest to the turn center. But I think you have to figure in the inside surface of the sponson as possibly having a little to do with the turning. (This would be a great test) Look at a cat boat. Or tunnels. No TF but only the sponson inside to get the boat through a turn. Granted a rigger has hardly any sponson in the water but I am thinking on the same lines.

More thinking......................... :unsure:

 

[Don Ferrette]

Now are we talking about a scale hydro or outrigger?? Both very different critters. Yeah, you might say I've built a scale or two.........

At any rate the turn fin placement as in the diagram has other variables as well- ride pads, how much dihedral, sponson tracking width, boat length, etc. :blink:

 

[BneHead]

Sorry Guys,

The boat is a Dumas Drag 'N Fly 20 hydro (shovelnose). Length is 28" and beam is 14". Not sure if you would call it a scale hydro, but it sure is no rigger. I've seen them place at both 1 and 2 on scratch build and pre-built RTR. I've seen them on most if not all the scale hydros (miss bud, etc). Also I know this is another topic, but it looks like it's split 50/50 about which side the rudder should be on..............Left or Right. Does it really matter? Is there any improvement in turning from one side to the other? My boat will be mainly turning right (as it is a hydro) but from time to time I think I'll let it turn left! LOL

Thanks Guys!!

 

[Grimracer]

I agree also that the best leverage would be closest to the turn center. But I think you have to figure in the inside surface of the sponson as possibly having a little to do with the turning. (This would be a great test) Look at a cat boat. Or tunnels. No TF but only the sponson inside to get the boat through a turn. Granted a rigger has hardly any sponson in the water but I am thinking on the same lines.

More thinking......................... :unsure:

Preston,

My thoughts were that the TF should be out bound for best leverage.. Did i say this wrong.. i should go look.. :blink:

In testing that i have done the keelson of the sponson is not nearly enough to rely on as a tuning aid. Indeed given enough pond the boat will negotiate a corner with out a TF. Lots of deadrise makes grims hydros slow...Bummer

However on tunnels (not sure about cats) we tune the turning through the design of the deadrise.

Bnehead

Looks like its a somewhat scale type of hull.. I would keep the TF outbound to avoid any lift on the hull from the water. If you want the boat to turn left it will do it (kind of) it will turn but just dont take your eye off the birdy.

Grim

 

[Don Ferrette]

Personally, I'd place it at position #1. If it was an outrigger it would be position #0 like Preston said. You've got to watch going too far outward as in position #2, it can make a boat dig too much in a corner since it drags more ride surface down as it bites in. B)