Only getting 12mph!?!

[nchogberg]

Hi Guys,

We seem to be getting less than desired performance from the 50hp Suzuki.

Previous owner put one of these props on that you can replace a blade if one breaks.

The factory prop is in the boat and has never been used. Still glossy black. I am going to put it on and check that out.

Any thoughts on this?

thanx...
Hawg

[DLT]

What are your RPMs?

That's about the best I do fully loaded: loaded up with people stuff for cruising, and full ballast.

But, RPMs are the key... If they are where there supposed to be, then you have the right pitch prop. Although, you may get somewhat better performance from a different design prop... Basically, on these boats, bigger blades are better...

[nchogberg]

I've been running 5K.

[DLT]

Is that within the recommended WOT range for your motor? If so, then you have the correct pitch.

If its low, then you need a bit less pitch.

If its high, then you need a bit more pitch.

One (of I'm sure many) rules of thumb is that 1 inch of pitch will give a somewhere near 200 RPM change. This can and will vary wildly. So, 1 inch really can give a change of just about anywhere near 100-300 RPM...

[Frank C]

The Suzuki 50 should spin right up to 6,800, so it sounds as if you're over-pitched.

No offense intended, but there are tons of previous threads. One by Mark K ran for the 5 months from May to October, was titled Michigan/Piranha/Solas Prop Test, Suzuki DF-50 on M, specifically discussing your motor. You'll have plenty of testing to do after you read his thread. Theoretically, your 2001 X should achieve just a bit more speed than Mark's 26M.

Search on [suzuki prop] and click "all terms" to find over 90 other threads.

[Bobby T.-26X #4767]

go with a 10 or 11 pitch prop with big dog ears (also known as a pontoon prop). also, for the Suzuki, it needs to be 11.75-12" diameter. anything smaller won't give you pushing power.
you want to get to 6100-6500 RPM's under normal loads.

bottom line...you need surface area and spin on that prop to push your big, heavy Mac with the small 50hp.

Bob T.
"DaBob"
'02X w/ '04 90-TLDI (14" x 11 pitch)
Dinghy Motor: '06 2.5-Suzuki

[baldbaby2000]

My boat goes faster with a prop that doesn't allow the desired rpm to be reached. My motor dealer told me I'll use more fuel that way.

[daver360]

Had a 11.5 x ? when I bought the boat with the suzuki df50. Only got about 12 mph max. Thought the boat was winding out too much at 6K. So I had it re-pitched to go less rpms. That was a mistake. I wrote here like you did and ended up buying a michigan wheel prop 11 3/4X 10. The rpms were just too much. Would go to rev limiter at 7300 rpms. But I got 17 mph with the tide and about 13 mph against the tide. I did trade the prop in at the prop shop for an 11 3/4 X 12. Thats what I was recommended by the salesman to slow it down to 6800 rpms. (have yet to try it) The df50 doesnt even wake up till after 6k which is within wot. And your boat will plane then. Sometimes I wish I got the tohatsu, but then again, the df50 sips gas when just going about 4500-5K and trolls nice.

[daver360]

Buy your new prop at a the local prop shop that will allow you to trade props in till you find the one you like. You will have a hard time trading it in if you buy one on the internet.

[Duane Dunn, Allegro]

I've looked at that type of props for years and have never found a brand that had a low enough pitch for an X. I run an 11.25 on my Tohatsu 50 and get 16.5 knots (18.9 mph) at WOT when I have the boat lightly loaded. Even with the 5 of us on board I hit 16 knots towing the kids on the inner tube.

Your RPM's are too low and your prop is too tall. You won't do your motor any good maxing out at only 5k. Go to a lower pitch that will get you at least 6500 rpm at WOT. There are some here who run prop pitches in the single digits with a 50HP. Use the WOT rpm as the guide for finding the right prop pitch. Also go as large a diameter as your motor will handle and consider a prop with a small amount of cupping.

[James V]

But I got 17 mph with the tide and about 13 mph against the tide.

Mmmmmmmmmmm. Are you useing your GPS for speed? If so, your tidal current speed is about 2 mph. So your actual boat speed on top of the water is 15mph. Still you should get a little more empty without ballest in smooth conditions.

I would go with the biggest prop as I could that would produce about 20% less than the max RPM's.

[eric3a]

..

[Duane Dunn, Allegro]

For those who want to convert,

One Statute Mile per hour is equal to one Nautical mile per hour * 1.15.

As far as I'm concerned everyone here should quote speeds in knots (Nautical miles per hour). If you have your gps set to statute miles you should change it to nautical miles.

But then you can bet that Roger's speed claims for the Mac are all measured in statute miles per hour because they make the marketing numbers look better.

Leave your fast boat ego behind and convert to knots.

[James V]

This forum has a lot new boat people and mph is easier to think with. I try to keep the boat words down because of this. This forum started out using MPH and the Mac promo uses MPH and most of my programs have both. I can convert easly enough but I do try to comunicate with others what they know best.

I personaly would like to keep the speed noted as mph because of this.

[beene]

One Statute Mile per hour is equal to one Nautical mile per hour * 1.15.

I think what you meant was:

1 Nautical Mile = 1.152 Statute Mile

ie 17kts = 19.6mph

But then again, I try to use Knots when refering to boating or flying.