Size of Emergency Outboard?

hyndlandguy · 27 July 2020, 08:24

I have an 8m Rib with a single o/b used mainly at sea off N.Cornwall. Thinking of carrying an emergency o/b in case main unit packs up.

Can anyone give any advise on what size / type to carry on board to get an 8m rib. Obviously nothing too bulky / heavy but big enough to do the job should it ever be needed.

Obsidian · 27 July 2020, 09:05

Hot topic this one! lol

What do you want to achieve?

With an 8m RIB you may only be able to manage some steering going with the prevailing wind/tide combo of the day, as to be able to fully navigate at 7kn could require quite a hefty lump.

How much power does your primary engine need to achieve 7kn against moderate wind and tide?

(I say 7kn because thats probably about your hull speed, ie before boat tries to climb onto the plane)

hyndlandguy · 27 July 2020, 09:09

I am just looking for the lightest and least bulky option to get the boat to safety if the main one stops working. Not looking to get on plane or anything like that, or go long distances. We use our rib inshore, usually within sight of land, and just considering having a plan B onboard should the main unit stop.

Ribtecer · 27 July 2020, 09:29

I've always understood as a rough rule of thumb, a hp of engine per metre of boat.

Striker · 27 July 2020, 10:31

I’ve got a transom mounted 4hp Yamaha 4 stroke on my 7mtr. Whilst it won’t push me through the 8knt current that runs through the swellies, it will give me steerage and keep me off the rocks / facing the right direction and will get me a lot closer to shore whilst I’m waiting for help.

It’s small enough to be mounted along side the primary on a liftable bracket without fouling.

It also has a self contained fuel tank plus a hose connection so I can run on clean fuel if there’s a problem, or switch over to the 200ltr hull tank - which will keep it running for a while....

Nos4r2 · 27 July 2020, 10:34

Ran an 8hp Yam 2stroke as an aux on my Ballistic 7.8, pushed it at 6 knots. You'll only ever get max displacement hull speed (about 6kts on an 8m) with an aux anyway.

Nos4r2 · 27 July 2020, 10:41

Incidentally, it's a short shaft as well, as it was sat to one side the prop was in clear water.
Meant I had a quick 2.9m sib as a tender

Maximus · 27 July 2020, 14:56

Quote:

Originally Posted by Ribtecer

I've always understood as a rough rule of thumb, a hp of engine per metre of boat.

x2
Anything a bit more is Fine....if the Transum will take it ..much less and you might struggle a bit especially fully loaded.
If it's out of site of land (especially if it's rough and off the beaten track)...always better to travel in company IMO.
Trouble is ...if it's REALLY Narly!....you'll soon loose site of each other and be on you're lonesome anyway!....

Fender · 27 July 2020, 15:18

Quote:

Originally Posted by hyndlandguy

I have an 8m Rib with a single o/b used mainly at sea off N.Cornwall. Thinking of carrying an emergency o/b in case main unit packs up.

Can anyone give any advise on what size / type to carry on board to get an 8m rib. Obviously nothing too bulky / heavy but big enough to do the job should it ever be needed.

Have a search on the forum, lots to read.................................

https://www.rib.net/forum/search.php?searchid=8814030