MacGregorSailors.com

I hesitate to start another prop thread, but I have an issue (feature, problem, whatever) that I haven't seen before in the forums. My 1996 with the BF50 maxes out at 9MPH at 5100 RPM WOT pretty much no matter what. Ballast in, pulling a wakeboard (that I built, but that's another thread), or ballast out with everyone (2 adults, 2 children) on board. The speed was verified via knotmeter and GPS. My prop is a 3 blade (I'm guessing stainless). The pictures don't show it but I can't find markings anywhere on the prop, including inside the hub, at least not while it is on the motor.




I'm not impressed with the bottom paint; it seems to do its job with regard to algea, but it isn't smooth (not like textured paint but not like a baby's butt either), and I wondered if that could be an issue.

From reading the other threads I wonder if I should switch to the Solas Amita 4 blade 11.8X9, part number 3313-118-09 per Erik Hardtle's post in another thread.

Sailing speeds aren't that great either (3-5 mph in plenty of wind) but that could just be they guy at the wheel .

I just throught it was strange that my speed didn't vary much whether I had ballast in or out, or even if I was/wasn't towing someone. I replaced the shift/throttle cables when I first got the boat, and I haven't tried lengthening them using the adjustment nut.

My goal is the highest top-end speed I can get. Any thoughts are appreciated.

I would investigate a few items:
1. Is the motor/prop positioned correctly on the boat? Search the forum and you will find a lot of info.
2. Can you pull a part number for the prop and add to your post? We can talk all day about the best props but unless we know what you have, it is all talk.
3. Suggest you borrow or buy another prop - it is possible the hub is spun on your prop. This condition will allow you to motor at slow speeds but will start slipping at higher speeds. I did this recently and could not make more than 5.5 knots no matter what rpm. I did this to my prop by fouling another boat's anchor line (the hub giving way is a way to protect the engine). I just bought a new SOLAS propeller and it gave me 2 knots better than the Evinrude one of the same dia/pitch.

Now THAT is quite interesting.

Which one - exactly - did you buy?

RobertB wrote:I just bought a new SOLAS propeller and it gave me 2 knots better than the Evinrude one of the same dia/pitch.

Aside from the prop, you need to ascertain whether or not the engine controls are set up correctly. It may be that you're not actually giving it full throttle, even though the control handle is full forward.

I'm on the road and can't send you the engine installation manual right now, but I've sent it to a couple of folks here already, so maybe someone else can. If not, I can send it in a couple of days.

A prop shop should be able to identify that prop, or at least accurately measure the pitch. The prop sizes mentioned seem to be very common on the BF50. Mine came with two 11-3/4 x 10 x 3-blade, and I recently put on an 11.8 x 9 x 4-blade Solas Amita, which I'm quite happy with. Not a big difference in high speed performance, but seat of the pants tells me it's better at pulling a wakeboard. Top engine speed is slightly higher than the OEM 3-blade, but that may have something to do with replacing the control cables and setting them up per the installation manual rather than the prop. Too many things changed at the same time to say which one had the biggest effect.

But the point is, most folks with the BF50 on an report around 16 mph SOG (per my GPS nav system) with no ballast, so you should be getting something in that general neighborhood.

I bought the http://www.iboats.com/Solas-Amita-3-Bla ... _id.477751

I had alot of trouble with the Evinrude thrust washer not being thick enough (found a thicker one at West Marine but still had to shim - suggest buying the thrust washer listed for the propeller.

The propeller shop guy also stated the SOLAS propellers are good.

If you're also having sailing performance problems that you don't attribute to a lack of skill, then you might also give some thought to how heavily loaded your boat typically is. Do you carry a lot of gear and typically load a lot of people? It may be that you're just pushing too much weight for the motor.

I would think that a spun prop would not get to 9mph. That's the least efficient speed for a Mac because it's smack dab in the middle of the "plowing" phase, before the boat is on a plan but while it's climbing its own bow wave. Just a little more power will get you right over that and to the 13 knot range because once you're on a plane the power curve flattens and you get some speed for "free" compared to the power it takes to plow.

Most likely you're over pitched by 3" and under diameter by 1 or 2". The prop looks like it may have been stock for a skiff rather than our heavier boats, although it's hard to tell scale in a photo.

mastreb wrote:I would think that a spun prop would not get to 9mph. That's the least efficient speed for a Mac because it's smack dab in the middle of the "plowing" phase, before the boat is on a plan but while it's climbing its own bow wave. Just a little more power will get you right over that and to the 13 knot range because once you're on a plane the power curve flattens and you get some speed for "free" compared to the power it takes to plow..

The 9 mph figure threw me off also - as I said, all I could manage was about 5.4 knots with my "modified" propeller.

From reading the other threads I wonder if I should switch to the Solas Amita 4 blade 11.8X9, part number 3313-118-09 per Erik Hardtle's post in another thread.

I have a basically new one in the original box from my BF50 that I kept when I sold the motor, PM me if interested.

I didn't read through all the post, but the prop size is behind that washer under the prop nut.

No wonder I couldn't find my post, I put it in the wrong forum!!!!! (I wonder if I can get the thread moved?) Nevertheless, great information from everyone.

I bought the Solas Amita 4 blade 11.8X9 - that was a mistake, I lost a knot! I took my "old" propeller home and cleaned it up, and found it was a stainless "PowerTech WBA-9", which is a 12" prop with 9" pitch. The info was stamped on the outside of the hub and I had to sand the crap off to find it. No wonder I lost speed, the propeller is smaller. As near as I can tell it is a $300 prop. Stupid of me not to ID it before buying another one.

When I had a spun prop on my 1967 Johnson 9.9 it would get to a certain speed and then "spin out" and I'd lose all thrust until I slowed down, just an FYI for anyone else that sees this behavior. I thought it was popping out of gear.

Load could be a factor. There is probably 800lbs in humans, 26 gallon fresh water tank, and a new galley (30-50 pounds probably), porta-potty, extra parts, tools, etc. I'm sure I'm at 1200 lbs payload. But I would think that if load were a factor dumping the ballast tank would make a difference. I cleaned up the blades with 220 grit wet/dry sandpaper but I don't have a lot of faith that's going to make a huge difference (any thoughts there?). The hub could still use some work but I'm not convinced it's worth the effort.

The anti-ventilation plate is even with the bottom of the boat, so I think that is right.

I cleaned off the bottom of the boat this weekend and confirmed that I had removed the trailer when putting it in the water, so that's not it.

The next thing I am going to try is adjusting the "throw" of the throttle cable (per tkanzler). Since I just threw one on there without any adjustment that seems a likely candidate for a problem. I downloaded the manual for that motor I think so I'll peruse that first, but I don't know if it has anything in particular with regard to the remote.

.....moved thread....Cat

tkanzler wrote:Aside from the prop, you need to ascertain whether or not the engine controls are set up correctly. It may be that you're not actually giving it full throttle, even though the control handle is full forward.

I'm on the road and can't send you the engine installation manual right now, but I've sent it to a couple of folks here already, so maybe someone else can. If not, I can send it in a couple of days.
.

Yes, I have the installation manual. If you want it, just send a message.

If you're also having sailing performance problems that you don't attribute to a lack of skill, then

Hey!! I resemble that remark......

I have the Amita 11.8x9 four blade on my 97 BF50 and get 16.5 mph empty ballast. I have 3 batteries, 65 quart frig, and about 400 lbs of gear with 425 lbs people.
I just don't like it singing between 2200-2800rpms. Does yours sing to?
Dave

alanmoor wrote:No wonder I couldn't find my post, I put it in the wrong forum!!!!! (I wonder if I can get the thread moved?) Nevertheless, great information from everyone.

I bought the Solas Amita 4 blade 11.8X9 - that was a mistake, I lost a knot! I took my "old" propeller home and cleaned it up, and found it was a stainless "PowerTech WBA-9", which is a 12" prop with 9" pitch. The info was stamped on the outside of the hub and I had to sand the crap off to find it. No wonder I lost speed, the propeller is smaller. As near as I can tell it is a $300 prop. Stupid of me not to ID it before buying another one.

When I had a spun prop on my 1967 Johnson 9.9 it would get to a certain speed and then "spin out" and I'd lose all thrust until I slowed down, just an FYI for anyone else that sees this behavior. I thought it was popping out of gear.

Load could be a factor. There is probably 800lbs in humans, 26 gallon fresh water tank, and a new galley (30-50 pounds probably), porta-potty, extra parts, tools, etc. I'm sure I'm at 1200 lbs payload. But I would think that if load were a factor dumping the ballast tank would make a difference. I cleaned up the blades with 220 grit wet/dry sandpaper but I don't have a lot of faith that's going to make a huge difference (any thoughts there?). The hub could still use some work but I'm not convinced it's worth the effort.

The anti-ventilation plate is even with the bottom of the boat, so I think that is right.

I cleaned off the bottom of the boat this weekend and confirmed that I had removed the trailer when putting it in the water, so that's not it.

The next thing I am going to try is adjusting the "throw" of the throttle cable (per tkanzler). Since I just threw one on there without any adjustment that seems a likely candidate for a problem. I downloaded the manual for that motor I think so I'll peruse that first, but I don't know if it has anything in particular with regard to the remote.

I can't really get above 10 mph with my 2000 2 stroke Nissan either, no matter the amount of load . I think its got the stock prop on. I just learned to live with it.