outboard speed?

jason22 · 04 September 2009, 21:16

Hi

Can any one tell me a rough idea on speed for a 2.5mtr to 3.2mtr inflatable rib for 2hp , 3ph , 10hp and a 15hp ?

I have`nt got a boat as yet but not sure what out board to go for as regarding speed.

Locozodiac · 04 September 2009, 21:24

Quote:

Originally Posted by jason22

Hi

Can any one tell me a rough idea on speed for a 2.5mtr to 3.2mtr inflatable rib for 2hp , 3ph , 10hp and a 15hp ?

I have`nt got a boat as yet but not sure what out board to go for as regarding speed.

For speed the largest 3.2 mtr rib with 15 Hp, should do minimum 35 + Km/h or slight more with flat calm waters, light weight, no wind.

jason22 · 04 September 2009, 21:34

Hi

I dont want to sound thick and dont no anything about boats but is 30mph in a car?

codprawn · 04 September 2009, 21:36

???

My 3.1m with a 15hp 4 stroke will do about 24mph - prob about 26 or 27 with a 2 stroke and a lighter load.

Locozodiac · 04 September 2009, 22:10

Quote:

Originally Posted by codprawn

???
prob about 26 or 27 with a 2 stroke and a lighter load.

Being a rib and not a sib probably, but might have my doubts, my 380 sib with 18 HP 2 strokes does near 40 Km/h which is about 25 mph in best conditions and 1 up.

Happy Sibbing

Locozodiac · 04 September 2009, 22:20

Quote:

Originally Posted by jason22

Hi

I dont want to sound thick and dont no anything about boats but is 30mph in a car?

Yes near 25 + mph in a car, may sound very low, but on water, the speed has a sensation of about 3 times the road speed sensation. Stick your amr in water to feel (joke)

Happy Sibbing

codprawn · 04 September 2009, 22:30

Quote:

Originally Posted by Locozodiac

Being a rib and not a sib probably, but might have my doubts, my 380 sib with 18 HP 2 strokes does near 40 Km/h which is about 25 mph in best conditions and 1 up.

Happy Sibbing

Sorry missed the RIB bit - I was on about a SIB!!!

Locozodiac · 05 September 2009, 00:23

Quote:

Originally Posted by codprawn

Sorry missed the RIB bit - I was on about a SIB!!!

Same size ribs/sibs, with same engines 15 HP; ribs should go slight faster, don't they ?

lightning · 05 September 2009, 01:02

My 2.8m Zodiac will do 14.5mph two up with my 6hp engine.

Fenlander · 06 September 2009, 12:42

I see you live near me Jason and know it's a fair trek to the sea. Wonder if you are thinking of sea or river use? If river an outboard up to 4hp will be fine.

My 3.2m wooden floor Zodiac with air keel will regularly make 16mph (seen on the GPS) and has seen a max of 19mph with its 9.8hp Tohatsu 2-stroke. That's with one adult and a 12yr old child.

David

jason22 · 06 September 2009, 18:37

Hi All

Thank you for your info , certainly got me thinking on the size of rib and out board to go for.
Would any one recommend ebay for a cheap rib or any were else?

jason22 · 06 September 2009, 18:41

Quote:

Originally Posted by Fenlander

I see you live near me Jason and know it's a fair trek to the sea. Wonder if you are thinking of sea or river use? If river an outboard up to 4hp will be fine.

My 3.2m wooden floor Zodiac with air keel will regularly make 16mph (seen on the GPS) and has seen a max of 19mph with its 9.8hp Tohatsu 2-stroke. That's with one adult and a 12yr old child.

David

Hi David

How far are you from Langtoft , market deeping?

I was thinking more lake / river for now.

Do you have any pictures?

jason

Fenlander · 06 September 2009, 19:53

I guess we're about 20mls south of you Jason. Here is our Zodiac in the shed as we bought it together with the Tohatsu we put on it. The Zodiac is 1971 but as new with no defects or patches.

Here it is in Scotland this year.

Again in Scotland with the kids heading out of the loch at around 15mph.

Hope that gives you some ideas.

By the way if you are going to licence your boat for river use have a look at the rates and see if over a certain horsepower makes a big difference to the cost.

Edit: I've just looked and an Ouse/Welland licence for our 3.2m Zodiac would be £63 if under 4hp (or £23 if you register it as manually propelled with an aux under 4hp) but with its 9.8hp motor a daft £227!!

David

jason22 · 06 September 2009, 21:27

Nice boat David

Hmm pay to go on a river , i did`nt think about that.

What is the diffrence between a rib and tender? as when i go away in the caravan i need to store it during traveling and i cant tow a trailer and a caravan.

MikeP · 07 September 2009, 10:48

3.1m Zodiac with 4HP 4-stroke outboard = 6.7MPH according to the GPS, with two adults, fuel tank and a bag of bits onboard (windlass would be the biggest weight in there, I think).

I've not played around with the trim yet to see if that helps squeeze anything more out of it at the top end.

Fenlander · 07 September 2009, 12:22

Interesting Mike that's about the max speed we get with 4 on board when the "overweight" prevents our 9.8hp pushing us onto the plane.

David

MikeP · 07 September 2009, 13:36

Indeed, I'm not 100% convinced whether we're out of displacement mode (not having any direct experience to compare to) and I'm also not sure whether I should expect anything more out of 4HP. At some point I want to plant the wife + vid camera on the bank whilst I zoom past at full tilt so that I've got something in pictures.

Fenlander · 07 September 2009, 14:33

Pretty sure you'll be in displacement mode at 6.7mph Mike. I've never watched the transition into planing on the GPS but would guess we do not plane (I'm talking 2 up now) until 10mph or perhaps a bit more. It's very noticeable as the boat lifts the bow sharply until it climbs the hump and levels out.

There are youtube videos of 3m inflatables and 4hp outboards planing but I bet you have to be one up with minimum weight and the inflatable nicely blown up. I had a 3.5hp Suzuki on mine last year and that certainly wouldn't get it on the plane.

Here is an image of the kids digging an uneconomic hole in the water just prior to planing speed. I guess they're doing about 8mph.

Photos are interesting and worth taking. We have a 4m grp boat as well and usually take both out together on the sea which gives a great chance to photograph how the they look in action.

BTW really enjoyed your Sharpness and Bristol Harbour reports.... might be tempted to do one on our activities.

A job move nearly brought us to your area last year but reluctance to move the kids at a crucial stage of life/schooling meant we didn't take it up. Access to salty water compared with where we are now was appealing though.

David

MikeP · 09 September 2009, 22:38

Thanks David, I really like to read other people's tales and exploits - I've been posting up my little trip reports to hopefully help future forum warriors (a) get into the hobby to start off with and; (b) not have to rehash the questions I've found myself asking (and not already found in a clear way searching through the forum to date).

You guys are definitely a premiere, No 1 resource, in the best tradition of internet forums. Long may it all continue.

chris123 · 11 September 2009, 17:14

Quote:

Originally Posted by MikeP

Indeed, I'm not 100% convinced whether we're out of displacement mode (not having any direct experience to compare to) and I'm also not sure whether I should expect anything more out of 4HP. At some point I want to plant the wife + vid camera on the bank whilst I zoom past at full tilt so that I've got something in pictures.

The switch from displacement to planing will be around 8 to 10 knots (maybe a bit lower for a little SIB).

If you are not sure if you are planing, you probably aren't

- it is very noticeable in a SIB - the bow will come down quite quickly until the boat is flat, there will be a surge of acceleration (if you keep the throttle in the same position your speed will jump by about 3 to 5 knots), and the ride will suddenly get smoother (assuming you are in smooth water).

Cheers

Chris