Propeller advice

Hi all,

New to the forum, restoring my childhood pride and joy an MFA spearfish. Simple task of new radio gear and ESC and clean up of the propshaft, but I also have an eye on a few spares and struggling to find a compatible propeller. I have one, but I'd like to have some spares - trouble is I can't find a threaded 3/16" prop anywhere on the internet. Seems modern boats use a drive cog and non threaded prop. Can anyone advise where I can get a threaded prop like the photo?

Thanks

Link to the right place will help!

https://www.prestwich.ndirect.co.uk/

Modern props work the same ‘threaded’ but usually now in m2,3,4,6 sizes.

Dog driven props are the modem equipment for the prop your looking to replace, you can simply buy the “dog” secure it to the shaft and the prop slots on after, use a lock nut to finish.

Other options are to get a smaller dia threaded prop  and re-tap the thread for your need at worse case...swap out the shaft of your boat to the modern equivalent size.

Admin

Setup for a modern shaft, using a dog drive to spin the prop....

Final option which I forgot, the prop shop...


https://www.prop-shop.co.uk/products.php?cat=general-purpose

The guy who used to run it, was able to make up custom props for you, if it’s not listed, it would be worth a phone call to ask if he can make up a prop for you with the correct thread.

Thanks for the replies, much appreciated. I had seen some threaded metric sized props but nothing 3/16. Eye-balling the dog drive I'm not sure I have the shaft length to install one, although I might just buy one to try. Is it possible to insert some sort of reducer into the proptube to convert it to M4? I'm not keen to remove the proptube it is well glassed in, last option might be to get a custom prop made!

I always glass in my shafts, removing them isn’t a huge deal ( most of the time a good whack with a hammer can loose em from the epoxy then just twist it out)
The last time I had to remove a shaft it required me to dremmel it out but nothing some new glass and p38 couldn’t fix after.

This of course is a extreme fix over buying some custom made up props, that said long term the original shaft the bushings maybe on there way out ( their only bronze) so although a shaft replacement seams excessive for a full restoration to give you years or hassle free leakage of the shaft and as well as being able to run the modern metric props it maybe worth consideration.

It maybe worth looking to see if a custom threaded prop can be made for you, and look if the price of a new shaft and some hard work can justify the shaft swap.

Most dog driven props run on an adapter which attaches to a flexi drive shaft, and the dog, prop and nut all fit on the end of that, this adapter is a square fit to the flexi shaft and not designed to fit on a threaded shaft... to that end, here’s one more suggestion...

Buy a length of stainless steel that is fitted for your current shaft tube cut and tap the ends one to fit your coupling size and the other to take M4 or M5 props effectively making a new shaft this is a very simple job and wouldn’t only cost a few quid, which leaves you options to take any of the standard two blades props or to use a dog drive...

Personally looking at the options making up a new shaft now seams the easier of all suggestions, and only requires the minimum of work to cut and tap.

Great advice thanks - Simon from the prop shop got back to me saying it's a simple job to make a prop the size I need and cheap enough so that will solve my issues and get me on the water for now. When I have more time on my hands I like your idea to make a new shaft with ends threaded to M4 - thanks again.

Keep us posted on your build/restoration I love older boats so would be nice to see a swordfish take shape on The forum!

Roadrunner wrote:

Keep us posted on your build/restoration I love older boats so would be nice to see a swordfish take shape on The forum!

I agree, the more timber classics on the water, especially part varnished the better.

I have 2 MFA Spearfish, one with a Merco 61 and the other is brushless

your propshaft is actually 2ba and modern M5 props fit it very well, I've had some off eBay and more from Cornwall Model Boats. The prop in your picture is an X53.5 which is what I have on the Merco 61, my brushless I've converted to dog drive with a replacement shaft and has a 35mm 1.4pitch bronze prop - I bought an unfinished kit so changing shaft was easy.

nhp651 wrote:

Roadrunner wrote:

Keep us posted on your build/restoration I love older boats so would be nice to see a swordfish take shape on The forum!

I agree, the more timber classics on the water, especially part varnished the better.

the Spearfish is all fibreglass

Well that's interesting, 2BA is 4.7mm which is what I'd measured with calipers, but since 3/16" was a common option on props for sale and is 4.76mm I'd assumed my shaft must be 3/16". Steve at the prop shop had proposed to make a bronze prop in 2BA for me so this should still work. When you say M5 props work well do they thread on tight despite them being slightly oversized?

Nice boats by the way and thanks for the videos - yes mine is also a fibreglass spearfish! Will be running the 12v MFA marlin motor it had 30 yrs ago to start with, might go brushless in the future. What brushless setup do you use?

Akamini wrote:

Well that's interesting, 2BA is 4.7mm which is what I'd measured with calipers, but since 3/16" was a common option on props for sale and is 4.76mm I'd assumed my shaft must be 3/16". Steve at the prop shop had proposed to make a bronze prop in 2BA for me so this should still work. When you say M5 props work well do they thread on tight despite them being slightly oversized?

Nice boats by the way and thanks for the videos - yes mine is also a fibreglass spearfish! Will be running the 12v MFA marlin motor it had 30 yrs ago to start with, might go brushless in the future. What brushless setup do you use?

M5 prop tightens perfectly fine - my Merco 61 hasn't been able to throw it off

The electric one has a XK 3674 2200kv motor with 150a ESC (both water cooled) with 3s 5ah LiPo's turning a 35mm bronze prop (glass filled nylon props fly apart before you get to the 24,000 odd RPM ) - with that setup I've had to limit the throttle to 80% in the transmitter. In the video I posted before it was on about a third throttle (so really about 25% of capability ish)

what version of Spearfish do you have? Both of mine are the early type with fixed cabin and smaller hatch while my friend has 3 and all his are the later type where the cabin comes off as a much larger hatch. My Merco one I bought as a new kit in the early 80's and has always had Merco 61 power, sadly the first one which is a early 1960's twin plug engine destroyed it's con-rod last year so the boat now has a 1970's replacement.

Where about's do you live?

I'm in sunny Glasgow so a long way from Southsea! Hoping to get out for a test voyage when the weather calms down, will try and post a video.

I'm not sure which version I have, was bought for me when I was a child I'd guess 1986-1988. Ran on a 6v decaperm initially which was a bit weak then changed to the MFA marlin 12v when they released it, cruises fine on that from memory but no speed machine. From your description I'd say mine is the early type, only the wooden rear hatch some off the cabin is fixed which makes working on it forward of the centre quite difficult.

Ordered a bronze 2BA 5214 custom prop, £25 and should last the next 30 years even if it goes brushless!

Just be sure to keep that nut tight to the prop, wouldn’t be the first time I threw a prop in the 30 squid zone and all due to not having that nut locked up tight enough!

Akamini wrote:

I'm in sunny Glasgow so a long way from Southsea! Hoping to get out for a test voyage when the weather calms down, will try and post a video.

I'm not sure which version I have, was bought for me when I was a child I'd guess 1986-1988. Ran on a 6v decaperm initially which was a bit weak then changed to the MFA marlin 12v when they released it, cruises fine on that from memory but no speed machine. From your description I'd say mine is the early type, only the wooden rear hatch some off the cabin is fixed which makes working on it forward of the centre quite difficult.

Ordered a bronze 2BA 5214 custom prop, £25 and should last the next 30 years even if it goes brushless!

My normal home is Annan (about 7 miles East of Gretna) and "local" lake is near Brampton just over the border near Carlisle, I'm temporally living in Portsmouth to enable my dad to live at home after an extended hospital stay. Where do you actually sail your boat? If it works out I could come up for a visit when next up.

you have the same version as mine, the smaller hatch is a pain on my Merco one - the only way to get to the fuel tank, throttle servo and remove the engine if needed is to remove the deck off the hull. I have the deck attached with Tiger Seal so it's fairly easy to cut round the seal, last year I had the deck off about 5/6 times

I don't really have a spot to sail yet, just getting this project finished! Took it out for a test at an old quarry nearby, went well - the old motor and heavy lead acid battery just as I remembered.