PeterMcK
New Member
Nick,
I hope my input is not too late for you.
I've a 1979 Moody 33 Mk 2 with the same shaft setup as you, i.e., limited swinging space for the prop.
I fitted a 12" dia x 8" pitch Radice a dozen or more years ago, replacing a fixed three-blade Lancing equipoise 12 x 6, which in turn replaced the original standard turbine pattern 12 x 8 two blade.
My engine was the original Thornycroft 90, maximum torque 70 Nm, running through the standard 1:1 TMP gearbox.
The Radice 12x8 gave adequate performance, up to almost 7 knots at 2500 rpm in flat water. Punching into biggish head seas, the boatspeed could be knocked down to 2 or 2.5 knots by ploughing into a big wave and would take a wee while to build up again. Astern performance was perfectly ok in my view, possibly something to do with the 1:1 gearing and the relatively high rotational speeds. There was practically no prop walk (by contrast, the fixed equipoise was like a stern thruster). Generally I was happy enough with it. (And as for drag under sail, well we won Class 1 of the 100 mile Scottish Two Handed Race against a fleet of mainly all-out racing machines two years running, amongst other joys.) Note, particularly for your purposes, this setup was most certainly NOT overpropped. I am very surprised, therefore, that you're being advised to go for a 12x7.
Your Beta 30 has a torque of about 60 Nm, and runs up to 3600 rpm, giving, through the 1.5:1 reduction, 90 Nm and a maximum of 2400 rpm at the prop. (Note that there's no point in trying to spin the 12 inch prop faster than about 2600 anyway; it just cavitates and thrashes.)
By comparison, the original Thornycroft 90 in the Moody 33 has a torque of about 70 Nm at the flywheel, and more or less the same at the prop through the 1:1 box (the fact that the T90 will run up to 3500 rpm is irrelevant; you can't run that prop beyond 2600 to any good effect). It seem to me that, based on my experience with the T90 and a Radice, even a 12x8 two blade Radice would be substantially underpropped on your new setup, never mind the 12x7 which has been recommended to you.
My latest move has been to re-engine, two years ago, with an ultra low hours Thornycroft 108, basically a bored out and otherwise improved version of the T90. The T108 has a torque of 105 Nm and feeds through my original 1:1 box. It was seriously underpropped when I tried it for a season with the Radice 12x8, even able to spin the prop up to full engine rpm with the boat tethered alongside. Obviously it would give the same boat performance as with the old engine but would not have exploited the 50% increase in torque available.
So .... based on some trials with the Radice 12x8, also with the fixed two blade and three blade props, and some calculations I've done including modelling hull resistance, I'm fitting 13x10 blades to the original Radice hub. (Sillette Sonic will supply a new pair of Radice blades for 60% of the price of the full propeller.)
I know I'm taking a bit of a chance that I'll have trouble with prop noise (but I doubt whether it'll make much difference), with clearance now down to just under an inch from the skeg but it's a relatively cheap experiment compared to all the other options. Unfortunately, I'm late this year and still two or three weeks away from launching so I won't be able to report till then.
As for corrosion, I've had absolutely no problem with the Radice. I always use a shaft anode but even so, every fixed prop I've owned has eventually shown some pitting. Also, after about 12 seasons use, the wear, if any, on my Radice gears and swivels was imperceptible.
The Radice looks clumsy but it seems to work and its is robust. I, too, thought about changing to a Flexofold two blade after reading the YM review (no Radice in the trial however). But then I came across a comparison in the French magazine, Voile, in which, according to my interpretation of the results, the Radice does a lot better than just OK, in fact, it appears to be among the better props in the trial in several important respects. (The testers' main point of criticism was to do with noise and vibration - I have to say that having last season switched between my Radice and, temporarily for test purposes, a new fixed three blader, I would have been hard pushed to tell them apart in that respect.) The Radice has the distinct advantage of being cheaper by far than the Flexofold or Gori. Its looks appear to belie its capability. But, quite literally, you pays your money ...
Concerning feathering props, there are three drawbacks, apart from cost. Firstly, the sailing drag is inevitably higher than for a folder. Secondly, the blades are flat, not twisted, and are therefore significantly compromised in terms of their motoring efficiency by comparison with a fixed prop or a folder. Thirdly (for Moody 33 applications) they tend not to be available in small sizes.
As for why there is no place on a sailing boat for a fixed propeller, the abstract, conclusions, table 4 and figures 6, 9a and 9b of this research paper highlight the main facts:
http://strathprints.strath.ac.uk/5670/1/strathprints005670.pdf
Voile report (for Radice):
http://www.klapschroef.nl/foto/14.pdf
YM report (for Flexofold and Varifold):
http://www.flexofold.com/upload_dir/docs/Test_YachtingMonthly_low.pdf
Peter
I hope my input is not too late for you.
I've a 1979 Moody 33 Mk 2 with the same shaft setup as you, i.e., limited swinging space for the prop.
I fitted a 12" dia x 8" pitch Radice a dozen or more years ago, replacing a fixed three-blade Lancing equipoise 12 x 6, which in turn replaced the original standard turbine pattern 12 x 8 two blade.
My engine was the original Thornycroft 90, maximum torque 70 Nm, running through the standard 1:1 TMP gearbox.
The Radice 12x8 gave adequate performance, up to almost 7 knots at 2500 rpm in flat water. Punching into biggish head seas, the boatspeed could be knocked down to 2 or 2.5 knots by ploughing into a big wave and would take a wee while to build up again. Astern performance was perfectly ok in my view, possibly something to do with the 1:1 gearing and the relatively high rotational speeds. There was practically no prop walk (by contrast, the fixed equipoise was like a stern thruster). Generally I was happy enough with it. (And as for drag under sail, well we won Class 1 of the 100 mile Scottish Two Handed Race against a fleet of mainly all-out racing machines two years running, amongst other joys.) Note, particularly for your purposes, this setup was most certainly NOT overpropped. I am very surprised, therefore, that you're being advised to go for a 12x7.
Your Beta 30 has a torque of about 60 Nm, and runs up to 3600 rpm, giving, through the 1.5:1 reduction, 90 Nm and a maximum of 2400 rpm at the prop. (Note that there's no point in trying to spin the 12 inch prop faster than about 2600 anyway; it just cavitates and thrashes.)
By comparison, the original Thornycroft 90 in the Moody 33 has a torque of about 70 Nm at the flywheel, and more or less the same at the prop through the 1:1 box (the fact that the T90 will run up to 3500 rpm is irrelevant; you can't run that prop beyond 2600 to any good effect). It seem to me that, based on my experience with the T90 and a Radice, even a 12x8 two blade Radice would be substantially underpropped on your new setup, never mind the 12x7 which has been recommended to you.
My latest move has been to re-engine, two years ago, with an ultra low hours Thornycroft 108, basically a bored out and otherwise improved version of the T90. The T108 has a torque of 105 Nm and feeds through my original 1:1 box. It was seriously underpropped when I tried it for a season with the Radice 12x8, even able to spin the prop up to full engine rpm with the boat tethered alongside. Obviously it would give the same boat performance as with the old engine but would not have exploited the 50% increase in torque available.
So .... based on some trials with the Radice 12x8, also with the fixed two blade and three blade props, and some calculations I've done including modelling hull resistance, I'm fitting 13x10 blades to the original Radice hub. (Sillette Sonic will supply a new pair of Radice blades for 60% of the price of the full propeller.)
I know I'm taking a bit of a chance that I'll have trouble with prop noise (but I doubt whether it'll make much difference), with clearance now down to just under an inch from the skeg but it's a relatively cheap experiment compared to all the other options. Unfortunately, I'm late this year and still two or three weeks away from launching so I won't be able to report till then.
As for corrosion, I've had absolutely no problem with the Radice. I always use a shaft anode but even so, every fixed prop I've owned has eventually shown some pitting. Also, after about 12 seasons use, the wear, if any, on my Radice gears and swivels was imperceptible.
The Radice looks clumsy but it seems to work and its is robust. I, too, thought about changing to a Flexofold two blade after reading the YM review (no Radice in the trial however). But then I came across a comparison in the French magazine, Voile, in which, according to my interpretation of the results, the Radice does a lot better than just OK, in fact, it appears to be among the better props in the trial in several important respects. (The testers' main point of criticism was to do with noise and vibration - I have to say that having last season switched between my Radice and, temporarily for test purposes, a new fixed three blader, I would have been hard pushed to tell them apart in that respect.) The Radice has the distinct advantage of being cheaper by far than the Flexofold or Gori. Its looks appear to belie its capability. But, quite literally, you pays your money ...
Concerning feathering props, there are three drawbacks, apart from cost. Firstly, the sailing drag is inevitably higher than for a folder. Secondly, the blades are flat, not twisted, and are therefore significantly compromised in terms of their motoring efficiency by comparison with a fixed prop or a folder. Thirdly (for Moody 33 applications) they tend not to be available in small sizes.
As for why there is no place on a sailing boat for a fixed propeller, the abstract, conclusions, table 4 and figures 6, 9a and 9b of this research paper highlight the main facts:
http://strathprints.strath.ac.uk/5670/1/strathprints005670.pdf
Voile report (for Radice):
http://www.klapschroef.nl/foto/14.pdf
YM report (for Flexofold and Varifold):
http://www.flexofold.com/upload_dir/docs/Test_YachtingMonthly_low.pdf
Peter
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