C275 under propped

Jul 24, 2018
34
Catalina 275 36 Sydney Harbour
Do any C275 owners think the boat comes underpropped?

From what I understand (I’m no expert but learning fast) a 5000lb 26’5” LWL D/L Ratio=121 monohull driven by a 14hp sail-drive should under power readily achieve hull speed. Mine doesn’t. On a glass calm day its Yanmar 2YM15 stretches all the way out to 3800rpm governor cut-off achieving only 6.3-6.4 knots through the water. In any case the set-up doesn’t quite ‘feel’ to have the right amount of bite relative to work-rate… I’m underpropped.

My boat came with a folding 2 blade 15/10 fixed, in place of (what I believe to be standard Catalina factory release) fixed 2 blade 14/11. At first I assumed the lesser pitch on the replacement folder was the issue. Due to potential long term issues associated with underworking the diesel / not wanting to ever be caught on a lee shore in a blow without enough drive to effectively get off / and just wanting to charge around the harbour more efficiently - I’m now looking into getting this sorted.

I definitely want to stick with a folder, but don’t have budget for an outright replacement folder/feathered. So I’m looking to replace blades on the existing Volvo stock during annual haul out this coming southern Spring.

In discussion with a diesel mechanic prop supplier, he explained a 15/10 should give at least a like performance to a 14/11 on basis the extra open blade diameter should make up for its lesser pitch (that opinion subsequently backed up by a 2nd prop supplier) so he was a bit surprised. I then sent him the attached data sheet for the boat, his thoughts are the boat might come out of the factory a bit underpropped on basis a 2YM15 shouldn’t quite rev to 3670rpms with the right amount of prop resistance. He suggested going for a bit of increased pitch - above 14/11 - to ensure I get a noticeable improvement and to justify the exercise.

To keep this economical I want to get replacement blades that achieve a result however at the same time without over-propping (and potentially setting myself up for long term issues in that direction). So I want to try and get this right first pass, done during ant-fouling and back in the water same day - without any follow up haul out remedial buggeration.

To that end... I’m curious to know from any other C275 owners (those with inboard auxiliary & saildrive):

What is your prop diameter/pitch? Are you getting 6.9-7.0 knots with it?

Cheers
 

Attachments

Azure

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Mar 5, 2017
27
Catalina 275 Sport 1 San Francisco
Roo, Congratulations on your purchase and thank you very much for your interesting additions to this forum. I have been considering a feathering prop and would also appreciate input. Thank you also for the attached file. I noticed that they used hull #1 for the test. I purchased hull #1. On my first sail I was very impressed with the speed of the boat. Unfortunately after testing the instruments, I found that the speed needed to be adjusted to lower setting. Don't know what they used for their test speed, but if they used the installed instruments, the results could be as much as one knot high.
 
Nov 8, 2007
1,523
Hunter 27_75-84 Sandusky Harbor Marina, Ohio
Roo, 6.4 knots sounds fine to me! I don’t think you will run into any situation where your current set-up would not be more than adequate.

On the other hand, it does sound like you could be a little under propped.

The key to any prop exercise is to get a good, competent prop shop to supply you. They should stand behind their calculations, and be willing to rework the prop pitch for free if they don’t get it right the first time.

Welcome to the forum, and good luck with your new boat.
 
Jul 24, 2018
34
Catalina 275 36 Sydney Harbour
Roo, 6.4 knots sounds fine to me! I don’t think you will run into any situation where your current set-up would not be more than adequate.

On the other hand, it does sound like you could be a little under propped.

The key to any prop exercise is to get a good, competent prop shop to supply you. They should stand behind their calculations, and be willing to rework the prop pitch for free if they don’t get it right the first time.
Bear in mind David, that 6.4kts was throttle lever flat to the floor on glass calm (running in the auxiliary whilst criss-crossing the harbour under moonlight). But your point is sound and I’ll admit to being a bit paranoid.

I grew up in Hobart port city of Tasmania in the roaring 40 latitudes - think of it as little more than a speed hump for prevailing westerlies of the Southern Ocean. Lost count the number of times I found myself sliding around the foredeck of my Dad’s boat in total darkness, a kid in his pyjamas desperately hanging on for dear life to some mysterious slimy mooring buoy in some remote forbidding anchorage, as the wind howled.

The front had arrived ahead of forecast, you see, (it happened all the time) so this unknown and uncharted mooring line could no longer be relied on to hold us for the night and we had to move. As a 7 - 9 year old I was convinced that if I lost grip on that thing before the glow plug alarm sounded… we were goners.

But the southerly buster bogeymen from my childhood can’t get me anymore, at least not in Sydney Harbour. Worrying now whether my C275 has enough prop pitch to rip out its own stern bollards in a tug-o-war with a marina is perhaps no different to that mysterious slimy buoy from my childhood. It’s time to ‘let it go’.

But I will take your welcome advice and make sure my prop guy specs the new blades without blinking + has no qualms about righting any wrongs if he over (or under) eggs it.
 
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Jul 24, 2018
34
Catalina 275 36 Sydney Harbour
Roo, Congratulations on your purchase and thank you very much for your interesting additions to this forum. I have been considering a feathering prop and would also appreciate input. Thank you also for the attached file. I noticed that they used hull #1 for the test. I purchased hull #1. On my first sail I was very impressed with the speed of the boat. Unfortunately after testing the instruments, I found that the speed needed to be adjusted to lower setting. Don't know what they used for their test speed, but if they used the installed instruments, the results could be as much as one knot high.
Azure, Thanks for the welcome + your rather intriguing revelation about hull #1 speedo. If the transducer was indeed 'optimistically' calibrated back during testing (think considerable industry praise on launch of the model [for reasons including performance]) I'm not a conspiracy theorist, but...

At the very lease it might support my thesis/paranoia that the boats possibly do come out of the shed with their 'iron topsail' a bit under-pitched.

We have no takers yet on my prop spec v speed disclosure challenge... but I will definitely be briefing my prop supplier to up anti a bit above standard issue14/11 for my replacement folding blades. Sapphire (hull #26) due to come out of the drink for a re-spray October/November. Will let you know how I get on.
 
Jun 6, 2016
204
Catalina 275 Wilmette, IL
I have been recently without a tranny (see "problems" shortly) and have not had a glass no-wind day so I can comment as of yet.

You should not put a lot of trust in Catalina's estimate of weight as they are notorious for under weighting their boats. So your numbers in your first post will be off. I now wish I got the center point lift to accurately weigh my boat (empty of course) as I believe the weight is 15% or more north of 5000 (mine, more because of the wing). This is something that Catalina could do easily, but they just rely on their "estimate".

I believe the standard fixed 2 blade is 14x11, but I don't recall seeing any numbers on it. I do know the diameter is definitely 14. The J/88, using the same engine and probably lighter, is suppose to be configured with a 2 blade 14x11 flex-o-fold prop. I believe flex-o-fold Denmark recommends 14x11 and the UK recommends 15x11. Unfortunately, this is not an exact science and to get peak performance, it may be a matter of trial and error. But if I was going to choose, it would be one of those two.
 
Mar 20, 2012
17
Hunter 28.5 leach lake Walker mn.
I replaced the factory installed fixed blade prop with a Flex-o-fold. I cant find the box/invoice now, but will get the size when I haul out in October. Having said that my 275 will max out at about 6.2 + knots and 3,300 to 3,400 RPM. the 3,800 RPM seems high to me.
 
Jul 24, 2018
34
Catalina 275 36 Sydney Harbour
I sent the boat and its auxiliary specs + aforementioned Yanmar performance report data sheet (based on a 14x11 prop) to Flexofold, they came back recommending 15x11. Unfortunately their quote with freight from Denmark to Oz is a bit beyond my budget to upgrade from one folder to another. If I was replacing outright from fixed to folder I would definitely go there (Flexofold composite hub looks a really nice product) however to be economical with what I have I'm still looking to retain my existing Volvo stock.

Unfortunately Volvo don't do two blade folders in 15x11... their next catalogued step up from my 15x10 blades are 16x10 which would be OTT.

...So I'm going to pay a local prop dealer workshop $300AUD to work my existing brass blades from 10 to 11 pitch during haul-out. It might mean a second days rent for a slip-yard space (or back out of the water briefly the following day) to re-attach the blades once they've been bent, but is looking to be considerably cheaper than replacing new the entire assembly. Keeping the exercise cheap shoul also de-risk any disappointment should I not quite get the result I'm after. Will see.

One re-occurring bit of advice I'm getting from everyone I've dealt with on this that I would pass on - and its surprised me a bit - is that there is no substitute for 'rubber on the road' so to speak. That is to say blade diameter is worth considerably more than pitch if you are looking to increase bite.
 
Jul 24, 2018
34
Catalina 275 36 Sydney Harbour
Sapphire prop.jpg

Sapphire went back in the water on Saturday (post annual haul out) with her Volvo Penta 2 blade folding blades bent from 15x10 to an increased 15x11 pitch. There was an immediate noticeable improvement, even at low revs reversing out of the wet birth. Previously getting 6.3-6.4 knots at 3800rpm/full throttle... she now does 6.5knots at 3400rpm and 7.2knots (wake just starting to separate) at 3700rpm/full throttle. She just feels lighter now under power in a lumpy sea-state.

So for $300AUD spent I'll get around a bit quicker, will have something in reserve if caught on a lee shore + will hopefully de-risk glazed bores to some extent longer term. No doubt the fresh hard coat of sprayed antifoul helped the cause on Saturday but truth be told I was diving the boat quite regularly to wipe and keep it relatively clean beforehand - so this was definitely the result I was after. Happy Days.