Protecting creatures and coral from propellers

[slboatdesing]

Obviously jet skis have a flush water inlet and no protruding propeller, but I could not find many other designs that mounted a propeller in a caged environment.

The only exception is having a propeller fixed between the twin hulls of a catamaran. Presumably a small boat fitted with a water jet would be able to operate in shallow water where jet skis are allowed.

A recessed propeller protected by a plate of some sort would work? It would work in reverse thrust as well, without any modification such as reverse buckets.

Tunnel thrusters seem to be the design I am looking for but are they unsuited for propulsion?

Images: Underside of an actual Jet-ski, and design for a recessed propeller.

 

[comfisherman]

Coral and the structure beneath it have a deleterious effect on hulls..... as such the best protection of coral is the same for the hull.... keep them as far apart as possible.

If your contacting hull up to the task.... maybe a shrouded outboard? Worked for the manatees..

 

[TANSL]

Much more dangerous than the propellers, for the marine fauna and flora, are the anchors of the boats.

 

[slboatdesing]

I will look at shrouded outboard. I was thinking of conventional propellers shielded by some sort of shroud. This retracting arrangement goes halfway there. The craft can be beached, however I cannot understand the swing keells.

"She is equipped with hydraulic operating swing keels and the minimal draught is 1.20 m (4 ft). With the swing keels and retractable motors lifted she can be beached."

African Cats launches GreenCat 605 Green-Motion with swing keels and electric retractable propulsion https://www.greencarcongress.com/2012/07/acats-20120713.html

Africancats.com https://www.africancats.com/pictures-greencat445

The arrangement in the attached image also shows a boat with a protected propeller and also can be beached?
The arrangement - the propeller fixed on a keel and a propeller protector underneath seems to be able to work, but can it bear the weight of the boat if it is used to drag the boat ashore?

There is a nice design here with the outboard motor in between two sides of the hull.

https://www.boatdesign.net/attachments/mell-cat-e-0154-engine-pod-jpg.80404/

In this thread:

Outboard motor transom design https://www.boatdesign.net/threads/outboard-motor-transom-design.46725/

 

[slboatdesing]

What I had in mind was an alternative to a jet motor - not using a compressor - just ordinary propellers. Clearly this can be done with a catamaran with electric podded motors or motor shafts and propellers inboard of the pontoons and covered by some sort of a a shroud. That will work fine. The image shows a conceptual diagram only, the dimensions need to be worked out. Some sort of a torpedo like drive would work better:

Candela's revolutionary new high-powered electric boat motors have 'almost unlimited lifetime' https://electrek.co/2021/08/19/candelas-revolutionary-new-high-powered-electric-boat-motors-have-almost-unlimited-lifetime/?fbclid=IwAR0eb_Yfk3Lud0SV9fUwRjZCRa5-gvUfpBxU1tgQ0VzRT5qc41SzseDPoi4


Protecting coral
Protecting sea creatures
Allowing operation in shallow waters
Allowing beaching without damage

There are one or two alternatives to jet skis. I will post them later if I find them.

Here is a design that uses what I call a 'chunnel motor' - it needs to be tested, and optimized if it is feasible. Its main advantages are that it does not need a compressor and can be operated in reverse. It does not have the jet effect but does have the recessed, protected installation. All it lacks is a sort of protective plate underneath. The motor will have to be lifted a little but will that make it a surface drive? A pod motor would fit nicely.

Clever designs here, all..

A 22 ft Fishing cat design https://www.boatdesign.net/threads/a-22-ft-fishing-cat-design.54666/

 

[slboatdesing]

As for anchors - I had no idea...wow. Will read on. Small boats don't use anchors thank God.

" On top of this, anchoring can cause serious damage to corals and other marine environments like seagrass beds. Even the most careful throw of an anchor can be devastating. In just one instance in Florida in 2019, critically endangered elkhorn corals, that had previously survived Hurricane Irma, were wiped out as a result of a dragged anchor.

Sadly, anchor damage to coral colonies isn’t uncommon. But it can be avoided. Read on to find out more about the impact anchoring has on the marine environment and what you can do to prevent anchor damage."

What Impact Does Anchoring Have on Marine Environments? — Pacific Asia Travel Association https://www.pata.org/blog/what-impact-does-anchoring-have-on-marine-environments

What about jet boating up streams?

This means PWC riders are disturbing more wildlife than any other craft. Fish, birds, dolphins and even whales have been disturbed or displaced by increasing PWC use in once-protected spaces.

Are personal watercraft destroying the planet? https://science.howstuffworks.com/environmental/green-science/watercraft-destroy-planet.htm

 

[TANSL]

Small boats don't use anchors thank God.

It is precisely the small boats, which anchor near the coast to bathe, that most damage the coastal seabed.

 

[slboatdesing]

I can only imagine what those anchors are doing to the sea floor. Thanks for the information.
There is also this: I don't mean to offend anyone's sport, but jetting upstream at 80kmh can it be ok for the environment, not to mention dragging the boat along the bottom.

 

[comfisherman]

Jet boats and the ground, small sailboats and coral reefs.... both do best when kept separate. Still going to argue the best response to coral prop interactions is to think through them enough to avoid them. Perk of coral is it's inanimate, makes it tough for it to sneak up on a mariner.

Had a local captain crack up on a rockpile near town. They were able to control down flooding and get to a haul out. The rocks proximity to town made the cracks in the engine room were smaller than the bruise to his ego. He wanted it repaired and a solution to what he determined was a hull to thin. Wild ideas as adding lots of glass to the inside beefing up the keel iron and cladding the bottom with steel. Shipyard manager humored each with rather eye watering quotes.

Eventually he slipped in a quote for a keyed watch alarm and a software update to his navigation and autopilot system that allowed a proximity alarm to a large external speaker. It was the 1,000$ solution to a perceived quarter million dollar problem.

Moral of the story, don't hit the coral. It will be happy and so will you.

 

[slboatdesing]

I guess it is all down to experience if you do not have expensive navigational equipment. Are the charts they have good enough? The ones that show shallow waters and rocks.

 

[DCockey]

Cages around propellers add significant drag. Many lobster boats in Maine have cages around the propeller to prevent the rope from a lobster trap to buoy from wrapping around the propeller.

Shrouded propellers are less efficient than unshrouded propellers for most conditions. An exception is slow vessel speed and high thrust.

 

[gonzo]

What you actually need is a GPS connected to a taser strapped to the boat operator. A good zap when he gets too close to corals. Otherwise, there is no technology to fix stupid.