MacGregorSailors.com

Hi there,

I hope someone might be able to shed some light on some performance issues I am having with my Mac 26M. I put her back in the water yesterday after the winter layup and this is my first experience with the mac as I bought it in December 2011, engine was serviced by me, new oils and filter, sparkplugs and cam belt and its a yamaha ft50get high thrust. I havent loaded it up with loads of stuff but do have a 30KG tender in side at the back.

I have filled the water ballast but the boat seems to sit a bit bow down so the plimsole line is not horizontal with the water, I dont understand this as there is no weight in the front at all, anyone have any ideas?

I took the boat out for a test run across a local bay (christchurch) and with a mill pond sea but I could only get 10 knots at 4200 rpm, pushing the engine to its maximum 4500rpm I managed 10.5 knots - both through the water (i.e. not GPS). there was no wind to speak of. Can anyone help with any tips on this as I was under the impression the M with a 50 HP could manage 15Knots?

Many thanks.

Gavin.

Welcome to the board...
Nose heavy ? These boats are usually aft heavy.. 4500 RPM @ WOT? Well short of MSMPS of about 5800 RPM IIRC
If you would add to your profile what year your boat is and which Yamaha you have it will help things a lot when trying to give answers.. As You see I have an 05 Merc 50 HP EFI BF .. I have fuel Injection and I must have a Prop somewhere between 13.5 inches and 14 inches..
Nose heavy humm check under the V Berth for " stuff" Prop size are you over proped? Most of us with BF Lower ends have a 10 to 12 Pitched prop

Divecoz wrote:Welcome to the board...
Nose heavy ? These boats are usually aft heavy.. 4500 RPM @ WOT? Well short of MSMPS of about 5800 RPM IIRC
If you would add to your profile what year your boat is and which Yamaha you have it will help things a lot when trying to give answers.. As You see I have an 05 Merc 50 HP EFI BF .. I have fuel Injection and I must have a Prop somewhere between 13.5 inches and 14 inches..
Nose heavy humm check under the V Berth for " stuff" Prop size are you over proped? Most of us with BF Lower ends have a 10 to 12 Pitched prop

Hi There, thanks for the reply i have nothing under the vbirth apart from the 3 sails which dont weigh much, i just re-read my outboard manual and it should max out at 5000-6000 rpm so for some reason the engine isnt reving high enough.... its a 13 inch prop - will update my profile, any ideas on the reasons why the engine wont rev up?

Gavman,

Bow low with ballast in is not that uncommon. My boat seems a little bow down with ballast in. I have seen pictures of other 26M's also looking a little bow down with ballast in. Not severe...but you can see the line is not level.

4500 RPM at WOT...Like Dive says -- maybe too big of a prop. I am not a prop expert.

My 40HP 2-Stroke Merc gets 5200 RPM at WOT with a 8x12 prop. And I can get 14 knots with ballast and 16.5 or so without.

Good luck and welcome to the club.

Cheers,
Jim

You maybe reading the prop as a 13 pitch, thats way to much for a 3-4 blade prop. Try a 3 blade 10 pitch prop, or a 4 blade 9 inch prop.
That will get you to the mid rpm's for your big foot 50.
Dave

gavman wrote:

Divecoz wrote:Welcome to the board...
Nose heavy ? These boats are usually aft heavy.. 4500 RPM @ WOT? Well short of MSMPS of about 5800 RPM IIRC
If you would add to your profile what year your boat is and which Yamaha you have it will help things a lot when trying to give answers.. As You see I have an 05 Merc 50 HP EFI BF .. I have fuel Injection and I must have a Prop somewhere between 13.5 inches and 14 inches..
Nose heavy humm check under the V Berth for " stuff" Prop size are you over proped? Most of us with BF Lower ends have a 10 to 12 Pitched prop

Hi There, thanks for the reply i have nothing under the vbirth apart from the 3 sails which dont weigh much, i just re-read my outboard manual and it should max out at 5000-6000 rpm so for some reason the engine isnt reving high enough.... its a 13 inch prop - will update my profile, any ideas on the reasons why the engine wont rev up?

Better gear heads than me on this board.. That said.. Big Foot should have 13.5 = 14 " Prop .. The Pitch should read somewhere between 10 = 12 Lots of 10's and 11 ' s being used on this board.. Does that Yammy have Carb's or EFI? Either way Check the plugs.. should be a light to med brown.. but no matter they should appear "pretty" clean.. Fresh Gas? or last years? Did you run it dry or let her sit.. how about the previous owner? Check for proper gap.. IMHO add a full can of Sea foam to a 6 gallon tank and run that motor.. out on the lake .. let her sit if you can over night and run her again tomorrow.. Cant do that and seeing as your NOT my neighbor !! Put a set of cooling muffs on the engine and run her at idle for 10 = 15 minutes and turn her off let her sit a couple hours and do that several times.. maybe over a couple days..
I assume that if you had test equipment suitable for testing for vacuum leaks and Spark Voltage you would have mentioned it already..At some point you may HAVE to take her to a Yammy Mechanic.. There is No Doubt an issue..

You will not achieve Warp Speed with the ballast tank full. Ballast tanks should be empty when using transdrive..

One cup of Earl Grey and don't hold the Cardasians!

Thanks for all the replies - lots to think about. I have emailed the previous owner to see what he used to get, i guess it could be prop size holding the revs back due to load. re empty tanks, the manual clearly states the tank should be full as there is a risk of capsize so i am concerned about emptying it.

The yamaha is an efi engine and the fuel is fresh, the prop stamp is 13 5/8 x 13-K, engine was winterised with fogging oil but i didnt run the fuel out and so i guess the fuel sat from Dec3rd to late feb when i serviced it and changed the cam belt. i was chatting to a friend of mine about it and it does feel like it want to power up between 4000 and 4500 but thats the limit of the remote control unit so he thought it could be throttle linkage which i need to look at.

Is there a rough consensus on the best prop for this engine and this boat as i know this engine wasnt the one that came with the boat from new as that was a 2 stroke, the the first owner swapped out straight away and perhaps this prop is too big or has too high a pitch and the load is preventing the revs from getting up?

Re the testing equipment for vacuum and voltage - big outboards are new to me so i havent done that - i guess a mechanic would need to get involved if all my other theories fail... Last boat had a big thumping diesel in it but that only did 5 knots - hence my current disappointment

also whats a BF lower end?

thanks

Gavin

gavman wrote:Thanks for all the replies - lots to think about. I have emailed the previous owner to see what he used to get, i guess it could be prop size holding the revs back due to load. re empty tanks, the manual clearly states the tank should be full as there is a risk of capsize so i am concerned about emptying it.

To each his own...but I think that warning is a little over-cautious.

I go full speed with ballast empty all the time. I make full speed, full deflection hard turns. The boat will lean over to like 40 degrees...lots of fun.

Motoring around "Slip Shape" -- this is a video of me doing a "high speed" pass by my friends boat this past summer. "High Speed" may be a bit of stretch but this was no ballast and you can see it lean over during the turns.

But I do these kind of things sensibly...everyone seated in cockpit, no wakes to cut through, fairly calm/still waters.

I will go full speed with empty ballast in a little bit more chop or through wakes but don't make high speed turns this way and try to take wakes/waves at close to 90 degrees.

When you get the opportunities and the conditions are favorable give ballast empty motoring a try. Just be sensible about it.

Cheers,
Jim

Thanks Jim - looks fun in your video. I will give it a try in the summer. I live on the southcoat of England and the Solent is notorious so I have to be a bit careful as the weather can whip up very quickly.

Figured out what BF means but it appears its a Mercury term so not sure if it applies to my yamaha or not. A local dealer reckons you loose 300rpm for each inch of pitch and so dropping from a 13 inch to an 11inch would see 600 rpm rise. Mercury say that you should achieve your wide open throttle figure with the right propeller and that is quoted as 5000-6000 for the Yamaha with max HP at 5500 rpm. does seem to suggest that the prop is too big.

appreciate any suggestions on prop size that work for other users out there.

Thanks

Gavin

Gavin,

I was stationed in London from 2007-2010. I took a 5-day liveaboard "Day Skipper" RYA course out of Hamble Pt in Feb 2008...chilly but lots of fun on that 38' boat. We visited most of the ports in the Solent.

And I took a 2-night trip down there and sailed with Rick Jones who is on the Isle just North of Cowes. He has a 26X. We tried to sail around the island and stopped for the night in Ventnor after going around clock-wise from Cowes. But the weather turned nasty so we didn't go to the South side but just motored back up into the Solent and sailed up there so more.

Great sailing grounds. And there is a Macgregor's Group in the UK with several Solent sailors I think.

Good luck.

Cheers,
Jim

BF Lower end = Big Foot Lower end = Bigger Gears Bigger Prop.. Ballast full ? I was always under the impression that referred to sailing.. and the full means NOT PARTIALLY .. Its That Partially Full that's makes it Dangerous..Roger runs those boats in the Video with empty ballast or he too would see much lower WOT speed.. Throttle linkage / Cable could be it , as well.. Take the hood off the motor and see if shes going stop to stop..
Fuel? How long was it in the fuel tank..? Not the engine the plastic portable tank. I dont believe any of us try to use fuel from one season to the next.. For me it goes in my Tractor and Snow blower at the end of every season.. ( for me ) I no longer carry all 24 gallons on board .. I dont use enough in a season, I now carry only about 15 gallons .. I have used Sea Foam Gas Additive for YEARS.. 2 stroke 4 Stroke and my Diesel EFI Carbs Cars Trucks Motorcycle.... Not All Additives are made the same and I have had GREAT SUCCESS with Sea Foam.. I dont even have to measure it..

Thanks Jim,

I have just joined the owners association and hope to meet up with some other owners. I am moored in christchurch river (Avon) and there are 2 others Macs moored near me so must try and meet the owners!


Re the prop issue....

I have just looked up in the service manual and the prop i have isnt even in the list of correct props!

I have 13 5/8 x 13-K

The prop in the manual for this engine should be 14 x 11 - K and is the only one listed for this engine.

Would anyone be able to tell me how different these props are? Does one provide more acceleration or more fuel efficiency or higher top speed.?

Cheers

Gavin.

As my wife noted on our honeymoon - "size matters"

gavman wrote:I have just looked up in the service manual and the prop i have isnt even in the list of correct props!

I have 13 5/8 x 13-K

The prop in the manual for this engine should be 14 x 11 - K and is the only one listed for this engine.

Gavin.