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Old 06 April 2008, 13:27   #1
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how fast do outboards go?

Hi Guys,

I am new here

I am very glad that i found these forums

I got some questions that i hope you can please answer

If i want to move 10 people in an inflatable or RIB then how many HP outboard would i need? I want to move at maximum 15 MPH.

I heard you can now get electric powered outboards, are they any good, fast?

One other thing, with a RIB do you inflate them yourself? Or is that only with inflatables.

You know in whitewater rafting are those boats inflatables or RIBS?

Really, i only want either of these boats for moving in calm water, up and down a bay, probably max 30 miles each way.

If you can please get back to me with some answers, sorry if i asked a lot,

any help much appreciated

Many many thanks
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Old 06 April 2008, 13:54   #2
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What exactly do you want to do with the boat? Where and why?
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Old 06 April 2008, 14:06   #3
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Welcome to RIBnet!

Quote:
Originally Posted by Nos4r2 View Post
What exactly do you want to do with the boat? Where and why?
or,

Hello Boatlover!

A first post is always a brave step! Your's asks a lot of questions and we'll (always!) have a lot of answers, often condradictory.... If you give us some idea what you're planning to do, we'll have more to go on. 30 miles is a fair lick in any craft. Many will be itching to inform you that RIBS/Inflatables have nothing in common with whitewater rafts, and they don't, despite superficial similarities (tubes). Let us know!
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Old 06 April 2008, 14:32   #4
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Hi

Many thanks for your replies guys

I am looking to just cruise a long the coast line, to be about no more than a quarter of a mile out from the shore. To go fifteen miles in one way and then refuel and come back another fifteen miles. I only want to go fifteen miles per hour and doubt i would be using it to pull a waterskier or wakeboarder. I would like to carry mainly five people on it, but some times would be taking 6, 8 or 10 people in total on board the boat. I would as well take some snorkel gear and a picnic box. The weight shouldn't be too much of an issue as i won't be carrying oxygen tanks for scuba diving as i'm only a snorkeler.

What can you suggest

Many thanks
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Old 06 April 2008, 14:35   #5
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to get us started on the answers.
  • outboards typically rotate at around 5000-6000 rpm
  • the gear box ratio is typically somewhere beteeen 1.8-2.5 ish
  • assuming the engine has sufficient power the top speed is then defined by the pitch of the propellor
most ribs (or sibs suitable for the people you want to put on it) will only start to plane [lift out the water] at 10-15 mph. Below that speed a rib may not be your best choice,
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Old 06 April 2008, 14:44   #6
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Level 1 course

Welcome to rib.net

I think from your questions that maybe you should consider a level 1 or even a level 2 course before you even venture 100 yards from the shore. Speak to a school before booking the course and discuss the boats you may use on the course. They will cover the merits of many types of craft that may be suited to your needs.

The level 1 course will introduce you to a variety of topics you may have never thought of and will improve your chances of staying alive, not having to call the lifeboat, knowing how to declare an emergency and MOST IMPORTANTLY YOUR & YOUR FAMILIES ENJOYMENT!!!!

FYI divers don't generally use Oxygen tanks as it is poisonous at only a shallow depth

Good luck and happy boating
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Old 06 April 2008, 14:53   #7
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Yup, that sounds like a nice way to spend an afternoon!

Any small RIB/Inflatable of around 5 metres or slightly smaller will cruise 5 up, with the minimal kit you list. 30 miles is fairly "do-able". I'm guessing, but a 50hp outboard should suffice to plane (ride over the water) at 15-20 miles an hour. 10 up is another matter and would require a larger craft of about 5.8m or more. Again, a disproportionately larger engine of perhaps 75 - 90hp would be needed, probably not worth your while?

Whatever kit you need, experience or training is even more important. The trip you mention is not a paddle in the kiddies pond. We can drown in 5 feet of water and proximity to the shore is not always a help - it's the thing we tend to wreck our boats on!

Best of luck with the plan!
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Old 06 April 2008, 14:56   #8
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I would agree with Karl - a course will widen your boating choices up and let you decide what you need (200 quid on a course is better that wasting money on the wrong boat, and you will be less likely to damage the boat or yourself). If you only want to do 15 kts then probably a rib is not what you want/need.

It might hurt a few people here to say it - but a "hard boat" may be better suited. Either way a boat which can confortably sit 10 will be quite big for a first boat.
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Old 06 April 2008, 15:09   #9
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True

Quote:
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FYI divers don't generally use Oxygen tanks as it is poisonous at only a shallow depth
Bang on, but as the Press often insist on calling them just that, what hope the rest of the mere mortals?
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Old 07 April 2008, 02:46   #10
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Bang on, but as the Press often insist on calling them just that, what hope the rest of the mere mortals?
Along with the other classics:

Bottles - something milk normally comes in.

Tanks - Used by Armies to keep troublesome civilians in check

Flippers - Name given to Dolphins

Pete
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Old 07 April 2008, 05:15   #11
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Quote:
Originally Posted by Boatlover View Post
Hi Guys,

I am new here
Hello and welcome. As Willk says, you'll almost get as many answers as replies to your post!!

Quote:
Originally Posted by Boatlover View Post
If i want to move 10 people in an inflatable or RIB then how many HP outboard would i need? I want to move at maximum 15 MPH.

I heard you can now get electric powered outboards, are they any good, fast?
That's a small question with a big answer, so I'll try to give an overview: 15mph is the sort of speed where a rib will "lift out" the water and skim across the surface rather than ploughing through the water like a ferry (think of it like skimming a flat stone off the beach). As a general rule, the more weight you have aboard (remember the "average" adult weights the best part of 80Kg) the more power you need to lift it out the water. So, you then need to have somewhere for these people to sit, store the fuel for your bigger engine etc and so the boat gets bigger and heavier...... As said above, you could easily be looking at 80+ HP to get a RIB for 10 "on the plane". Having said that, if you are happy toddling along watching the scenery drift by, a much smaller engine will do the job as you will be staying "in" the water, and so a RIB will probably not be the best thing to use. For that kind of trip a small inboard 2 cyl diesel in a "workboat" type hull may be a far more comfortable and infinitely more fuel efficient way of travelling.

Forget electric - you will need half a ton of batteries to manage that distance!

Quote:
Originally Posted by Boatlover View Post
One other thing, with a RIB do you inflate them yourself? Or is that only with inflatables.

You know in whitewater rafting are those boats inflatables or RIBS?
Unless you have a willing volunteer to hand, yes, you inflate yourself just like a white water raft.

There are essentially three types of inflatable boat:
1) White water raft type - the inflatable tube goes all the way round, nowhere to attatch an outboard, and the floor is "floppy" and made form the same material as the tubes. Power comes from the paddles.
2) "SIB". A bit like the raft, but with a small inflatable "keel" and a plywood transom at the back to fix an outboard engine to. The inflatable keel keeps the underside of the boat "rigid" and the bottom of the hull taught to allow it to plane. Very bouncy ride in waves, and usually nowhere to sit except the tube round the edge.
3) RIB - Essentially a solid boat with an inflatable tube round the sides. Again a solid transom to hang an engine from. Bigger RIBS can have inboard engines, usually diesel. The solid floor gives better handling through the waves than a SIB, but can't be deflated & rolled up for starage. The Tubes give bouyancy & stability when not on the plane, but generally are lifted clear of the water when moving fast which reduces drag.

Quote:
Originally Posted by Boatlover View Post
any help much appreciated

Many many thanks
I would second all the "get on a course" posts - that way you will get a better feel for what's out there and what the various boat types are capable of. The "Sportsboat" Certificate (at risk of showing my age ) used to have a "displacelment craft" subsection - any of you insructor types know is that is still the case?

Also you'll need to take into account how you plan to store the boat. For example I am limited in size because I keep mine in my garage, so instantly most of the RIBs out there are too wide to go through the door. If, however you keep it in a Marina / storage yard that's not a problem.......

My initial reaction would be that if there's normally only 5 of you, work out how often you'll have 9 aboard. Mine's 5m long and plated to carry 9 , but there wouldn't be a lot of room! If 10 is only occasional there may be a way round it by having 2 propellors - essentially a "high geared" one for when there's 5 of you and a "low geared" one for hauling 10 bods through the water, but more about that later......

Don't worry about asking more questions, coz that's why we're here - to exchange knowledge. And let's face it we've all probably just created more questions than we've answered!

Oops. That post got a bit long........
Cheers.
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Old 07 April 2008, 07:33   #12
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Quote:
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or,

Hello Boatlover!

A first post is always a brave step! Your's asks a lot of questions and we'll (always!) have a lot of answers, often condradictory.... If you give us some idea what you're planning to do, we'll have more to go on. 30 miles is a fair lick in any craft. Many will be itching to inform you that RIBS/Inflatables have nothing in common with whitewater rafts, and they don't, despite superficial similarities (tubes). Let us know!
Well said. Another arrogant comment from one of the "ribnet mafia"
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Old 07 April 2008, 08:13   #13
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Go for the largest HP engine the sib/rib factory recommends (see atached transom plate) if you would like to get the best performance out of it, a real danger to inflate sibs/ribs with air tanks, too much pressure, only permited with prudence on boats that have automatic pressure relief valves. Get a good electric inflator and a manometer.

Happy Boating
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