Prop shroud/protection devices?

rbcoomer

rbcoomer

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www.swfbr.org.uk
Does anyone here have any first hand experience with any of the aftermarket prop protection devices? (good or bad :o)

I've seen a number of such devices from the 'professional' (e.g. Prop Guard) to the home-made variants made with a tube of stainless! I recognise all the proviso's about attaching things to outboards, warranty implications etc, but my outboard is old and has hydrofoils fitted already (before I got it) so no real concerns on that front. FWIW, the hydrofoils do seem to work well and boat climbs easily onto plane at lower speeds than other similar ones I've seen, so although I probably wouldn't have thought to add them, they seem to pay dividends.

My main interest was for protecting against damage at low speed in shallow water. We want to use our boat primarily for local exploration (coastal and rivers) and whilst I have fitted a depth gauge, there is always a risk of nudging something solid when getting 'in close' for photographs, disembarking etc. As I don't have any power-trim/tilt, lifting the outboard to increase clearance isn't the easiest task.

In addition however, there are various claims on the more credible versions about improved thrust and handling, better economy etc! I can see how this would work and I'm not in any way disputing such claims, but curious as to why with rising fuel prices, such devices aren't more common or even fitted as standard if they offer so much improvement? Are they more prone to fouling for example or are costs/patent licensing fees prohibiting factors? Or is it simply that these offer best savings at lower speeds and most Mobo's are run at WOT? :eek::D

I'm looking to move to a bigger boat with a petrol inboard in the next 12-18 months, so fuel cost will undoubtedly become an issue - thus the current one (with old tired outboard) would make a good testing ground if I'm going to try!

Thanks in advance,

Robin
 
I use heavy duty custom prop guards on my outboard powered workboats rbc, because of the types of jobs they do, clearing log jams etc. Planing performance is reduced, but as they rarely plane, it doesn't matter.

From what I've seen, debris like small stones, sticks and rope will still get drawn into the vortex pulling water towards the prop when in gear.
Ours are fully caged/grilled, front and back with solid sides, but with 1" or 25mm gaps in the SS grills, the small debris makes it through.
It does keep the big stuff out though, which is the job required.

If you decide to go down this track and install a SS model, be aware that unless you insulate the different metals when attaching the guard to the alloy leg, a reaction will occur.
 
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Thanks Andie - interesting comments! I'm curious you've found them detrimental to planing - I suppose I assumed from the various claims that it would be similar or even improved? But hence the reason for asking on here - good honest answers - unless we're talking contentious issues like anchors of course... :rolleyes:

I think if I try one it would be one of the durable plastic variants, but appreciate the corrosion comments - thanks. I was surprised to see that most of these have little in the way of grill etc to prevent ingress of foreign objects and hence my question about fouling. I can envisage significant quantities of weed etc finding it's way into the prop!

Thankfully I won't be clearing log jams as I think my boat would rapidly convert to GRP pulp! :eek:
 
I've seen light duty versions surrounding props on surf-lifesaving ribs, but never questioned their performance.

Regardless of whatever you decide to fit, I would still try to exercise caution when probing around shallow water.
 
prop protection

If you track down my recent River Arun thread the last chapters (Pulborough and Pallingham) show that even with long keel, single shaft and a protected (by skeg), prop, expensive damage can happen to us creek-crawlers.
In six years I've been lifted out three times for prop repair and/or shaft replacement!
But I still recommend a NA diesel on a single shaft.
Good luck.
 
I fitted two club safety boats (Honda 80 4 strokers) with an aftermarket propguards. They did slow the Rib a bit on top speed. Steering on low speed seemed to be a bit improved. The boats were worked from a tidal harbour, getting up the river at low tide, shallow water over mussel beds/stoney sand was still a problem with debris sucked into nozzle.
 
Thanks - very useful feedback as always :)

Not sure if I'll try a guard yet as the primary reason was to protect prop and save potentially costly repairs, but with only a 30hp on a 14' I don't really want to reduce top speed. :rolleyes: Although boat planes from around 15kts, she won't do much more than about 25kts flat out.

I'm not planning on dinging the prop at all, but they do seem somewhat exposed and as I'm neither familiar with boats or local waters it's probably a matter of time... :o I'll have to exercise extra caution in the meanwhile and use the boat-hook to probe for obstructions when 'up close & personal' with shore/riverbanks! :D
 
I wouldn't beleive any of the makers' claims about increased economy etc for the cage type. Find something of similar chape, attach to a stick, and dangle it over the side submerged at 25 knots - feel the force of the drag!

I hate the things

If you are exploring very shallow and rocky waters you have to be careful withthe o/b anyway. If you hit a rock you can bust the skeg off and do other damage, aside from dinging the prop. So the cage wont mean you have to be any less carefull.

Just imho
 
Thanks, I'm thinking perhaps cash would be better invested in a spare prop if one pops up cheap on eBay! :D I was less concerned about skeg etc on the basis of very slow speed in these circumstances, but even then I guess damage is possible. The prop seemed most vulnerable due to rotational speeds. It doesn't sound like these devices will be worthwhile for me as things are however, but I'll keep in mind for future and just be extra careful (or fit a glass bottom to boat :rolleyes:)
 
This is just a random, left field thought, because you obviously are thinking about a larger boat in the future and will need a dinghy, and a reason to go shopping :).

If you try and source a good second-hand little outboard, like the trusty 3.3 Merc. 2 stroke, and mount it on an adjustable aux. bracket on the transom, it could be not only be auxilary power for you, but also a shallow water propulsion option.
Tilt up the main engine, and sneak along with the little mix-master just below the water surface at a couple of knots. Take a couple of spare split pins for the prop to shaft connection (they are designed to break on impact) and you will be able to go anywhere the boat hull will float.
Take the little motor with you to the next boat for the dinghy or a 'keep you off the rocks' option for the main boat. They weigh only 13kgs and store nicely in side pockets.
 
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AndieMac said:
This is just a random, left field thought, because you obviously are thinking about a larger boat in the future and will need a dinghy, and a reason to go shopping :).

If you try and source a good second-hand little outboard, like the trusty 3.3 Merc. 2 stroke, and mount it on an adjustable aux. bracket on the transom, it could be not only be auxilary power for you, but also a shallow water propulsion option.
Tilt up the main engine, and sneak along with the little mix-master just below the water surface at a couple of knots. Take a couple of spare split pins for the prop to shaft connection (they are designed to break on impact) and you will be able to go anywhere the boat hull will float.
Take the little motor with you to the next boat for the dinghy or a 'keep you off the rocks' option for the main boat. They weigh only 13kgs and store nicely in side pockets.
Click to expand...

Thanks Andie,

I had considered an auxiliary motor, but as current boat is small the space and weight are issues. I've found/made space for fenders, paddles, boat hook, flares, small toolbox, usual ropes, anchor, first aid, etc etc, but once we add a picnic & dry clothes etc a 14' boat seems more like 3'! :eek: There's only myself, SWMBO and our son (7), but definitely more cosy than spacious. :D

I did investigate electric outboards as I thought one would be suitable for emergency and river use, but feedback from forums was 'not enough oomph' for emergency use. In all honesty however, by the time I've added another battery, the weight wouldn't be much less than a small auxiliary anyway. I hadn't appreciated that the small unit props were designed with shear pins, so that's clearly a plus and easier than swapping main prop in the event of a bump on something hard.

With regards to up sizing, I can't see us going big enough to need a dingy, but could be wrong... :rolleyes: I'm hoping to get something in the 18-21' range with inboard and a cuddy - probably an early Fletcher Arrowbolt or similar. I'd like one at low initial cost that I can restore over a year or two as we gain experience in the 14' first - and then switch when we look to extend our exploration range. Whatever we move up to would need to be trailer-sized as mooring/berthing fees would be prohibitive. We also live on a very busy road and reversing a boat into drive would be hell. I can however drive in and then turn a trailer not exceeding 8M LOA - which equates to about 21' of boat maximum. (We've done it with an old 21' caravan I use for my office!)

A small outboard would probably be the way forward even if it transpires it's not big enough for next boat, I can always p/x nearer the time. I just need to investigate how much room there is for another bracket on transom...
 
Thanks for the feedback. I did pick up an auxiliary outboard for the ArrowFlyte in the early part of the summer and have since also acquired a bigger 21' project.

I can see the idea/benefit behind the improved skeg, and on a relatively flat bottom it could provide good deal of extra protection. Cost could be prohibitive over here however as in 'rip off Britain', $100 usually translates to about £150 with a 'marine' keyword surcharge of 20% and then a further 20% for HM Government... :mad: The other issue is the areas that I was concerned about were rivers with very random rock/mud and where a glancing side impact would be as likely as a bottom hit - hence the thought of the prop-shroud etc. I haven't gone any further with this idea so far.

For the project boat, being a bit less limited on space and because we are looking to go further afield and at night etc, I have invested in a decent echo-sounder/chart-plotter combination so we should get a better picture of the bottom anyway. :D When I send the existing prop on this one off for a refurb (has a few nibbles out of it!), I'll probably look to get a spare to keep in the boat too. This one won't be ready for the water for another 6-8 months or more and thereafter I'm not yet sure if we'll keep the 14' or not, but if so I will revisit this at a later date.
 
jfm said:
I wouldn't beleive any of the makers' claims about increased economy etc for the cage type. Find something of similar chape, attach to a stick, and dangle it over the side submerged at 25 knots - feel the force of the drag!

I hate the things

If you are exploring very shallow and rocky waters you have to be careful withthe o/b anyway. If you hit a rock you can bust the skeg off and do other damage, aside from dinging the prop. So the cage wont mean you have to be any less carefull.

Just imho
Click to expand...

jfm you seem to know it all. Any part of the boat or motor that touches the water creates drag. My boats runs 72mph trimmed out. It runs 70 since i added the Blackfin not to mention the oyster bed and bridge iron damage i escaped. I'll take that all day.
 
BLACKFIN88 said:
My boats runs 72mph trimmed out. It runs 70 since i added the Blackfin
Click to expand...
Huh? Since it's easy to guess from your alias that you have something to see with the product, I'd be curious to hear if you would call that a performance improvement, as stated in the website.
It would be easy to argue also about the stern lift, based on simple physics, but let's stick to performance: you can say it's worth suffering the speed reduction because of this and that, but you can't say that a speed reduction is a performance improvement, in my simple mind... :confused:
 
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