which folding Prop for Mk1 Moody 33

[Hoist]

Before anyone says it I am not joing the MOA

Anybody have any recommendations on which folding prop for a Mk1 Primrose Moody 33

Cheers

 

[Daydream believer]

Join the MOA. they will know
You know it makes sense

 

[Hoist]

Nope been there done that.

Don’t own a moody and don’t like the fact they don’t like you helping people who haven’t paid…

 

[Daydream believer]

Nope been there done that.

Don’t own a moody and don’t like the fact they don’t like you helping people who haven’t paid…

So you want to ponce off us for free instead?

 

[Tranona]

Before anyone says it I am not joing the MOA

Anybody have any recommendations on which folding prop for a Mk1 Primrose Moody 33

Cheers

Impossible to say without knowing what engine and gearbox is fitted. Provide that and I can calculate it for you - but if you are investing in a new one best to speak to Darglow Engineering and they will sell you the correct size Flexofold 2 blade. Be aware that not all folding props are the same, and though it is easy to calculate a size based on a standard 2 blade fixed, folders often are different because of the shapes and sizes different makers use, so buying used can be aa bit of a lottery not only finding the correct size, but also the correct diameter and taper.

The Moody 33 MK1 is a difficult boat for propellers as it has a very shallow propshaft angle and a 1.1 reduction resulting in a small propeller, usually 11 or 12" diameter which severely limits the choice of propeller type. However some have been re--engined with longer shaft and P bracket further aft to allow a larger diameter propeller. Normally a boat that size/displacement with a 30hp engine would have a 2:1 reduction and a 15 or 16" propeller.

 

[Hoist]

So you want to ponce off us for free instead?

Thanks for your input very helpful and informative.

You would do well on the MOA forum

 

[Daydream believer]

Thanks for your input very helpful and informative.

You would do well on the MOA forum

But it was free - no charge whatsoever.
But if you take liberties, I may have to submit a small charge

 

[Snowgoose-1]

After getting the right diameter and pitch right , is there a way of calculating the DAR , the actual area of the blades ? or is it just a compromise to minimise drag when sailing ?

There is often a wide selection of types on power boats, even among the non planing hulls.

 

[Tranona]

After getting the right diameter and pitch right , is there a way of calculating the DAR , the actual area of the blades ? or is it just a compromise to minimise drag when sailing ?

There is often a wide selection of types on power boats, even among the non planing hulls.

A typical DAR for a fixed 3 blade prop for a sailing auxiliary would be around 0.45 and a fixed 2 blade 0.25, although some are smaller than this to reduce drag under sail. Generally folding and feathering propellers have a larger DAR because drag under sail is no longer an issue

 

[AntarcticPilot]

After getting the right diameter and pitch right , is there a way of calculating the DAR , the actual area of the blades ? or is it just a compromise to minimise drag when sailing ?

There is often a wide selection of types on power boats, even among the non planing hulls.

See DAR measurement

 

[Hoist]

It's either a 2:1 or a 1:1. I will have my friend and prospective Moody owner check at the weekend.

A bit of googling revealed a few things I had suspected

"The Moody 33 is very restricted in the diameter of the prop. Think the maximum is 13".

Also

"Agree with Robmcg but I wonder if the prop is too big and he's getting turbulence around the hull which reduces efficiency? IIRC on my old Moody 33 the original prop was 2 blade 12" diameter and I changed to 3 blade 13" which made a huge improvement. I could have, just about, got a 14" diameter on her but with virtually no clearance at the hull. Best to talk to one of the prop makers as they're usually very helpful.
For what it's worth I think you will find the Thornycroft T90 is only rated at about 27HP in these boats. Very confusing but in the literature I had the engine was capable of 39HP but only delivered 27HP in that set up.
Hopefully someone with a M33 now will be along soon"

And

"I've done some experimenting with a Mk 2 (T'croft 90 + TMP 1:1) and found the following:
i) 12x8 Radice folding two blade (my current setup) gives adequate motoring performance (max 7 knots), is well matched to engine characteristics, is essential if you want to race; BUT fuel consumption up by 50% compared to 3-blade, progress about 3 knots into F8;
ii) 12x8 fixed two blade not much difference from folder except for the increased drag;
iii)12x6 Lansing 'Equipoise' 3-blade is slightly over pitched but gives hull speed at 2000rpm, 6.5 knots at 1500, is not expensive, can drive the boat hard (too hard if you're not careful) into full gale and big seas; downside is there's quite a lot of prop-walk astern (good once you're used to it) and it's no use if you want to race (handicap compensation isn't adequate).

Don't be taken in by the arguments for folders and feathering props if you're only cruising. The large blade area Lansing prop has the biggest drag of those I've used but it's still only worth about 0.2 to 0.3 of a knot on the sailing performance at 6.5 knots and certainly not the 0.5 to 1 knot you see bandied about."

DO CHECK THAT YOU'VE A REDUCTION BOX. For cruising, and assuming you've the 1:1 box, I'd go for a plain round bladed 12x6 three-blader which probably has less prop-walk than mine and is even cheaper."

These are all really old posts. I tried to find the mentioned Lansing Equipoise prop but found nothing. Radice and Gori still available through silette and really not that pricey new but sadly it's only the 2 blade props that are in the budget



There is a second hand Kiwi prop on ebay that might be an option. that would give the boat a 3 blade folder and adjustable pitch.

 

[Tranona]

Unlikely you will be able to fit a Kiwi in - the minimum diameter is 14.5" and most common are 16". The 12" Radice is pretty basic and the Moody needs more oomph if it is used for cruising and would have been fitted with 3 bladed probably 11" or 2 blade 12" when new. It is overpowered with the T90 engine - as one of comments show you can get hull speed (7 knots) at little over 2000rpm (the hull only requires 24hp for hull speed). Personally I would stick with a fixed blade.

 

[Hoist]

Thanks Tranona. I failed to spot that!

If we can get a cheap folder second hand we will give it a bash but failing that a new fixed will have to do the job.

Its a very budget operation. I'm a racer so the idea of having a fixed prop is totally alien to me!

I did find this flexfold which was fitted to a fulmar but at 14x8 its just a hair too big!

Pardon our interruption...

 

[Daydream believer]

- as one of comments show you can get hull speed (7 knots) at little over 2000rpm (the hull only requires 24hp for hull speed). Personally I would stick with a fixed blade.

Only asking, because I admit that I do not know the tech details
-But surely that is flat water. A bit of chop kills it dead & then one needs a lot more from the prop.
24 HP at the engine would possibly only be 8 hp at the prop. So all the more reason for a more powerful engine.
Then one can prop it to give the thrust needed in rougher conditions

 

[Daydream believer]

Thanks Tranona. I failed to spot that!

If we can get a cheap folder second hand we will give it a bash but failing that a new fixed will have to do the job.

Its a very budget operation. I'm a racer so the idea of having a fixed prop is totally alien to me!

I did find this flexfold which was fitted to a fulmar but at 14x8 its just a hair too big!

Pardon our interruption...

If you have the power in the engine to drive it then I would suggest that you go for it.
What HP is a T90 engine?

 

[Hoist]

Been told 35hp

as per the some of the posts i found from 20 years ago some people say its 27hp.

 

[Daydream believer]

My 31 ft Hanse had an MD 2020 (19HP) which with the saildrive fixed prop gave cruising speed at 2200 RPM of 5.9 kts. Max 6.8 in the canals.
I changed to a Brunton Autoprop & could only get 3 kts in a typical 1 M chop that one would see on the east coast round the Thames. Max revs would be 2800 as it seemed over propped. The engine only gives 6 HP at the prop.
In June 2023 I changed to a D1-30, 30 HP & the boat is transformed.( this suits me due to my disability meaning I may not be able to sail so may just have to motor) Same prop. Cruising speed 6.5kts @ circa 2200 rpm.in typical .5-.75 M high swell. Max speed in flattish water 7.5 kts.
I motored all the way to Ostend last year & had 2.5 high waves around the Longsand head & round the West Hinder & towards Ostend over the banks I was still doing 6.5kts by using max throttle. Waves were not too close together, for a change & not quite head on but rough all the same. Journey 13.5 hours from Bradwell tied up to enter the harbour. But it did use a lot more fuel.
So it is worth having the power to give that punch when needed & the prop to use it.