Boat Speed Update

[philfin]

Further to my recent post and the very helpful advice I recieved, I thought I would give you a wee bit of an update.

The issue was I could barely make 5.5 - 6 knts no matter how high th engine reved and it would rev freely. 43' Oceanis.

Did a lot of investigation, spoke to previous owner, supplier of Prop (Max Prop), consulted Max prop liretaure etc.
Discovered that previous owner had "adjusted" tinkered about with the pitch when he fitted it. General concensus seemed to think that pitch/blade angle should be in the region of 22 - 24 deg.

So boat up now and prop off this morning. Low and behold, set at 18 deg.

Going to adjust to 22 deg, change cutlass bearing, antifoul and back in early next week. Hoping for a couple more kts at 2,400 revs. Fingers crossed....

Should make a big diffence when having to motor on a typical 90-100 mile passage. 12hrs instead of 16hrs

 

[Oldhand]

Be careful 4 degrees is a large change to do in one go.

Mine was 22 degrees when I got my boat and it needed loads of revs just to make steerage way into wind, to the extent I sometimes thought it wasn't in gear. I increased it to 24 degrees and it is now perfect - engine reaches 50 rpm under max intermittent which is 150 rpm over max continuous. Any more pitch and it probably wouldn't reach max continuous rpm, that's what you need to check after you have done the change, with the prop clean of course.

Hope 24 degrees works for you as it does for me, depends on your boat and engine.

 

[philfin]

Aye, thanks. I will check for the max revs, continous and intermittent. Your right 4 deg is a lot in one go but I really believe that i am way under at the mo at 18 deg. Some folk are suggesting 24 deg but that would mean a 6 deg change in one go. Too much I think. So bearing in mind that I can only go up in 2 deg increments and I want to try and avoid taking boat up and down, I'm going to have a stab at it. Afterall its all a bit trial and error from what i can gather. I take your point about the big diffence 2 deg it made to your boat. What size and engine are we talking about?

 

[Sailfree]

Basically a correctly sized fixed prop must give the max speed as the blade are shaped. A feathering prop will not give the max forward speed as the blades are flat and not shaped for max forwards efficiency but they are better going astern as the shaped fixed prop is then more inefficient!

Can you rev freely at max revs? If yes prop pitch or size could be too small.

I woulds set the pitch to whats recommended and while 4 deg seems a large movement its not if they are currently set 4 deg wrong!!

Sad about having to always lift the boat to adjust the pitch on the max prop. That why I prefer the Variprop where it is adjusted from outside the propeller and can be done on a dive.
Aquastream, Kiwi and J props all adjustable from outside.

 

[Sy-Revolution]

....erm, I need to tweek my Variprop, how does one measure the pitch angle?

 

[Sailfree]

If you take off the anode they stamp on lines for the correct theoretical pitch angle movement range , sometimes they benefit from a slight adjustment after running for 1 year.

I increased mine by 1 deg forward as I wanted more power low down, found it was under pitched.

Must confess Paul Bell of 1st Marine Propulsion came out and did mine at no charge and just happened to have a new anode with him - now why do I always go back to them to buy my props!!. Contact Paul on 023 80 225944 and I am sure he will talk you through it and give you Variprops website that hasspecific instructions. No connection etc just received good service and competitive quotes.

IIRC 1 turn on the external grub screw (undo lock nut) gives an extra 1/2 deg of pitch. But I do get saga moments!!

Each engine boat combination is individual but as I can still get max revs (3800) from my Yanmar without any sign of labouring I am tempted to increase my forward pitch angle even more. For 75hp I went for the 4 bladed one for smoothness that only Variprop do!