Scrubbing speed in the turns

[Watercadet]

The Boat: Maus spt 20, N/R SS, OPS nitro pipe @ 8 3/4, 60% nitro, MC 9, AB x438, SS turn fin unknown,

strut about 7/8 hull to c/l of strut under boat, not off the transom, .5* negative trim.

Problem: Boat runs like a bat out of hell down the straights but will come off the pipe if I stay tight like in

lanes4,3,2,1. Comming out of the corner it is kinda slow to get back on the pipe, then back to bat out of hell.

Max rudder deflction is 25* but will hold lane 1 with 1/2 steering. If I make a wide turn (outside of lane 4) it

scrubs off a lot of speed but doesn't come off the pipe. Boat does get better by lap 4 but not all the way.

Pipe legnth has gone from 7 7/8 to 8 7/8. It will throttle on the straights where it is now. I have gone from

so lean that it takes a plug, to so rich that it will not ever get on the pipe at 8 7/8~9"

Pictures of set up here.

It is a long boat @ 33" and about the same weight at a nice PT 20 in my club.

What ya think is killing it in the corners?

 

[shoboat]

Adam,

Too much cup on the X438 propeller, even stock they need less. The front L.E. could

use a little trim also,this will help with the lack of RPM in the corners. I would try a

better 180 header also, the one you have on the boat looks pretty radical flow wise.

Good Luck,

Mark Sholund

 

[Watercadet]

Mark, how much cup should I pull out of it you think? Maybe a X437/3? I am gunna need to give you a call for the right blade anyway. The header is the only one I could get to stay inside the cowl cleanly. I had a N/R one on there to begin with, and the peformance was the same.

 

[shoboat]

Adam,

I just measured a stock X-438 @3.91" of cup. I would bring it down to 3.46" or less 3.21" of cup,

and shorten your pipe with less cup. You will turn more RPM=SPEED. That is a pretty big

turnfin on that boat,so I assume it holds in the turns quite well?

Keep Testing,

Mark Sholund

 

[Mark Anderson]

A 438 seems tiny for a N.R. when I ran one of these boats my Nova easily turned a 1445. You say it gets better as you run the boat. Seems like you have too much prop weight with a full tank. As you burn off fuel it moves the c.g. forward and there is less prop weight. Idealy you want the fuel on the c.g. so as you burn fuel it does not change the boat ride. If I remember right I used a four once tank shoved under both sides of the deck on the c.g. and no sump.

 

[Watercadet]

A 438 seems tiny for a N.R. when I ran one of these boats my Nova easily turned a 1445. You say it gets better as you run the boat. Seems like you have too much prop weight with a full tank. As you burn off fuel it moves the c.g. forward and there is less prop weight. Idealy you want the fuel on the c.g. so as you burn fuel it does not change the boat ride. If I remember right I used a four once tank shoved under both sides of the deck on the c.g. and no sump.

I thought if I took much more prop out of it, it was going to explode... You are right, the main tank is behind the CG. I will try the 4 oz ers under the deck. Do you think the 1445 would be a good choice with the right weight setup? The boat doesn't drag it's ass too bad but I think a little more lift wouldn't hurt a boat this long.

 

[anthony_marquart]

Is the turn fin angled down so that the right sponson is digging in while in the corners... I've had that before..

 

[Watercadet]

Is the turn fin angled down so that the right sponson is digging in while in the corners... I've had that before..

The fin is straight with the hull and the bends are paralell with the waterline at running attitude. It is huge like Mark noticed, but the boat has no tendancy to pull inside on the straight.

 

[Mark Anderson]

Mine ran 52mph with a 1445 with a Nova Rossi and ops pipe. The fin looks right to me. When you get the tanks relocated watch the boat as it gets into the turn. If the transom is settling it will load the prop. If this is the case shim the rudder bracket at the bottom to angle the blade slightly back at the bottom. 1-2 degrees should do it. This will cause the rudder to lift the transom in the turns slightly. If it wants to get up on the nose do exactly the opposite. You need to shim the bracket so it angles the pivot pin not just kick the blade back. I use shims made by ernst manufacturing from the hobby shop. They come in 1,2 and 3 degree.

 

[Watercadet]

Mine ran 52mph with a 1445 with a Nova Rossi and ops pipe. The fin looks right to me. When you get the tanks relocated watch the boat as it gets into the turn. If the transom is settling it will load the prop. If this is the case shim the rudder bracket at the bottom to angle the blade slightly back at the bottom. 1-2 degrees should do it. This will cause the rudder to lift the transom in the turns slightly. If it wants to get up on the nose do exactly the opposite. You need to shim the bracket so it angles the pivot pin not just kick the blade back. I use shims made by ernst manufacturing from the hobby shop. They come in 1,2 and 3 degree.

That is great info Mark! Thanks a ton

 

[Brian Blazer]

Pinch the waterline...you may be getting too much.

Brian

 

[Watercadet]

Pinch the waterline...you may be getting too much.

Brian

Thanks Brian. I put a zip tie on the pick up line and restricted it down to almost nill and fattened it up a bit that is when it started running better at the end of the heat. It was 85* air temp that day, but the water was in the 60's