BFN prop clearance improvement

Is there a chunk of wood in the rudder port?

The dark spot at the very back will be repaired. It is an imperfection during the original lay up. It is polyester resin spot with no glass in it.
bj

It may reduce the rooster tail a little but we do not beleive it will change the performance or handling much. Gary, (The Wizard) made the modification just to improve on the gap between the prop and the hull. A larger space between the prop and hull will minimize any vibration. The rule of thumb is: The distance between the prop and hull should be 10% of the diameter of the prop. Having the 79 and the 81 both there for comparison made it a modification easily done in an afternoon
bj

A few years later and I've finally decided to go for it on this "notched keel" mod. Again, all 81-90 direct drive BFN's got notched keels from the factory, as did all of the v-drive excel/bfn's 91-94. I think the primary purpose of the notch was to increase prop clearance. The original 13" diameter Federal was very tight (<1/2" hull clearance) on our '79 (pre-notch) BFN. Later (notched) BFN's ran 14" diameter props.

Last "before" shot:



Marked at 1/2":


Notched:


I started out with my HF power planer, but that was a little slow going even set at max depth... Probably due to the abuse its suffered. Then it died, so onto plan B- 40 grit flap discs on my angle grinder. Made a huge mess (dust) but took that 1/2" of thickness off quickly. Still need to smooth with a block and then fill in any remaining low spots... Then it'll be time to cut the recess for the rudder port. I have a good router, but any thoughts on specific bits, or how to make and attach a jig would be appreciated. Otherwise I'll be free handing it and then touching it up with thickened resin afterwards.

I am eager to see the differences in the boat's performance afterwards... My main hope is that this improves steering effort at speed. Even after taking all the weight out of our 79, converting to a new "2001" style long-travel steering cable and trying 2 different 11a rudders, it still takes significant effort (sometimes 2 hands) to crank the wheel over at higher speeds- the faster you go, the harder it is to crank over. Pinky finger easy at idle, so there is something else at play. Other early (pre-87) BFN's turn much easier, so I'm hoping that raising the rudder 1/2" or so changes that dynamic.

Other wish-list improvements would be a wake improvement (less washy lip) and an improvement (or at least no detriment) to top end speed. We shall see.

I'm having a bit of a hard time understanding this, but by removing the built up section for the rudder port notch, is the rudder port now not recessed?

Correct Bruce... I still need to re-cut the recess for the port.

Like this Pete?

Pete, I am not up speed on the terminology you're using... Got a link that explains the basics? Or pics of a "multi flute" cutter? Google image search results aren't consistent.

I think I'm getting the gist though... I'll bring the port home, make a jig or 2 and make a few practice cuts with the router once I get it back. I'll probably need new bits so feel free to recommend some, else I'll swing by HD and see what they have.

Tim,
I only mentioned a radius in the bottom of the pocket because it's common practice to reduce a stress point from a sharp corner by using a radius. The pocket would need to be oversize so the port base doesn't hit the radius. The gap can then be filled in with bedding compound (4200).

TRBenj wrote:

Looking at that picture Tim and wondering if you have the engine or trans out by the looks of that shaft? Sure must be hard with all the dust and the position you have to be in to get this done. Seem to remember you reinforced that area with this in mind when you replaced all the stringers too. Nice winters project.

DrCC wrote: I like BJ's idea of the gradual or radiused notch behind the strut.   Seems like it would be less likely to create an air pocket.

Tim mentioned the steps in the X55 which are right angled to the bottom as well. They, just like steps on a hydro or the stepped racers back in the 20's and 30's, increase speed by reducing drag on the hull bottom (air). But, there is a drawback at least on the X55. The rudder will cavitate at about 80% throttle making a turn to port. The boat flattens out, heads straight ahead and does not respond to the rudder position. Scary and the only thing to do is chop the power. When our ski club had the stripped down X, we actually have to reverse the show course from counterclockwise to clockwise!!

Gary, that's what minimizing strut to prop clearance looks like.

Actually, the trans is wintering in the Finger Lakes as it was popping out of gear and slipping under load (again). Still awaiting Dr Joe's diagnosis, but it may be necessary to go to a 10-18 if the 72c can't be saved.

Al, I should have reviewed this thread before I made my cut, it looks like BJ stopped his notch well short of the factory version and sloped it more gradually. My intention was to put the hard 90 step in the same place the factory started the slope (in effect, leaving extra material on the hull), thus giving myself the option to soften that feature later. it sounds like cavitation and rudder stall may be the downsides to look out for. Indeed, I had the stepped hull feature on the brain when I decided to go sharp. Seems some hull features are most effective (less sticky) when sharp... Maybe this particular feature is not a good candidate for that line of thinking. We shall see. I have other hull mods in mind and this hull is no show winner anyways... So it won't be getting any finishing touches (ie, gelcoat) anytime soon. Plenty of opportunities to make more changes if need be.

I spent some time on my back today with a block and 60 grit paper trying the get the area smoother... I'm still not there. More aggressive paper would be helpful, I may order some. Sanding upside down with dust raining down on you sucks, I'm ready for this project to be over! I did discover a bit of delam on one edge of the notch, so the grinder will have to come back out. One step forward, 2 steps back it seems, ha.

backfoot100 wrote: All I can say is WOW!!!!! Outstanding work but something I don't think I could bring myself to undertake. Very interesting to follow along on this one.

Eddie,
But you did such a fantastic job on the AS cradle!!

Tim,
I don't like Kevin's idea (sorry Kevin) using the rotary files. They won't take enough off in one pass. You may get about .020" with each cut so it would take many passes to get the roughly 3/8" deep pocket. It's as you know a real PITA working overhead. Holding that router for about 20 passes may get tough!