how fast is your rib?

[magiccity]

Gave it another run after some yamalube and the 100hr service and hit 41 with two adults, 5 year old and a fullly loaded 30 liter yeti.

[rnwright1969]

I feel awfully inadequate....37kn in a 5.4m sea-rider fitted with an old 90hp two smoke mariner...loaded with two guys and dive gear for 4 dives in total sooooo 120kg of associated crap.
That's with a 17 pitch prop, fitting a 19 pitch this weekend so watch this space, oh and a 'rolling sea' and 4200rpm

[simonl]

Originally Posted by rnwright1969

I feel awfully inadequate....37kn in a 5.4m sea-rider fitted with an old 90hp two smoke mariner...

You need to learn to lie then. General slipway chat proves definitively that 70-90 Hp engines, mostly 20+ years old, are the fastest things on the water. Using a transit to tow typically makes them go at least 5-10 mph quicker too, for some as-yet unknown reason.

[simonl]

Originally Posted by rnwright1969

I feel awfully inadequate....37kn in a 5.4m sea-rider fitted with an old 90hp two smoke mariner...

You need to learn to lie then. General slipway chat proves definitively that 70-90 Hp engines, mostly 20+ years old, are the fastest things on the water. Using a transit to tow typically makes them go at least 5-10 mph quicker too, for some as-yet unknown reason.

[Bigquick2010]

Thought you guys might enjoy this rib retube of How It's properly done. It's a long video but it was worth it. This boat is not only beautiful it is the fastest rib I've driven to date.

https://youtu.be/2uJfr42fano

[rnwright1969]

Originally Posted by simonl

You need to learn to lie then. General slipway chat proves definitively that 70-90 Hp engines, mostly 20+ years old, are the fastest things on the water. Using a transit to tow typically makes them go at least 5-10 mph quicker too, for some as-yet unknown reason.

I already have the flat-bed tranny and am considering fitting a HIAB to try and get it up to the fabled fifty, what do you reckon?

[longjohn]

Originally Posted by Leapy

Wow! 48mph with only 70hp. Impressive

I'm finding that hard to believe

[xchsurfers]

Originally Posted by Burtox

Ribcraft 585 with a four stroke Honda 90 will do 36MPH on the flat with a crew of 2.

This boat weighs more than a small planet. When I cut some holes in the console they were over 8mm thick. It is a nice solid boat and handles the sea better than me

what do you think I should get out Ribcraft 585 with a merc 150 optimax

[xchsurfers]

What do you think I should get from a Ribcraft 585 with a merc 150hp Optimax
It would only pull 5000 revs on a 19inch prop

[jonp]

My daughter recently got sponsorship from a boatbuilding company that build high speed boats for competing spearfishing people who seem to have very deep pockets and an addiction to speed. The last comp she entered she got to us their latest Kevlar creation on its first open water trial, a light weight 20ft missile with the latest 350 supercharged verado.

For me this something I never want to do again, speeds of over 70 knots in sloppy conditions meant simply holding on as I watched our gear either fly overboard or end in broken pieces at the back of the boat. I'll be sticking with my little zodiac cruising around at 20knots, by the way my daughter loved the 70knt machine.

[simonl]

Originally Posted by xchsurfers

What do you think I should get from a Ribcraft 585 with a merc 150hp Optimax
It would only pull 5000 revs on a 19inch prop

My guess- 46mph

[rnwright1969]

Had a blast out in my other boat 'Calypso', not a RIB but a dory complete with fully overhauled (just done) late generation 90hp.......


46.7kn that's going WOT against the last knockings of a flooding tide, running the opposite direction gave me near as damn it the same!

[simonl]

Originally Posted by rnwright1969

Had a blast out in my other boat 'Calypso', not a RIB but a dory complete with fully overhauled (just done) late generation 90hp.......


46.7kn that's going WOT against the last knockings of a flooding tide, running the opposite direction gave me near as damn it the same!

I assume there was no boat in the water?
That'll have several people wondering what they are doing wrong, not least me. Could you add some detail to help put it into context a bit more?
1. What size dory?
2. How did you measure speed?
3. How may revs?
4. What size prop?

[rnwright1969]

Very little boat in the water, which was flat calm!


The boat info is on the RIB base but............
6.0m
On two plotters, both within 0.5kn (photo on rib base)
No rev counter on this one, flat out and allowed to 'settle'
Currently 21 prop
Only self and wife with one 30ltr fuel tank, nowt else


I am 'relatively' confident about the speed as the same devices give an accurate speed for the Searider, well significantly slower than many (most) others on this site.


Oh also just had the HIAB fitted to my flatbed transit so bound to be really fast.....

[simonl]

I think 2 x GPS should give a pretty good level of confidence... but own up - you took the reading from the faster one didn't you?!

[rnwright1969]

No, strangely enough I didn't! I think the faster one was about 0.3kn faster, certainly nowhere near 1.0kn!


Oh and knowing what a 'shooting gallery' this particular thread is I wanted to make sure that the speed tied up with the plotter photographed, even though some guys think that the plotter speeds are suspect, I guess they wouldn't credit a chicken with an egg unless they saw it coming out!


Anyway another blast in the searider later this week with a higher pitch prop and less weight on-board to see if I can get above a very steady 37kn, fingers crossed!

[simonl]

Not sure how anyone can question high speeds on a plotter or any gps device with a good signal, which everything at sea should have. When it knows your position to within 10m (or much less), and it has a clock more accurate than we can imagine, it's just speed = distance/time. At walking speeds maybe it's a bit wobbly. When it's showing 46.6kts continuously I expect you're WAY better than 0.5kt accuracy; probably 0.1kt.

This is only a 2D model though, and you were of course well above sea level for that speed!

[rnwright1969]

Aaaaah, but there were two 2D models so that makes it 4D!!

[AndyFresh]

Dragged the missus out with me today as it was a good day to get a comparison on props for new boat. Thats almost as bad as my mate Pete taking his missus to the coal mining museum....I did treat her to lunch though!

Heres the stats
Xs700 Suzuki DF200 V6 full tank 160l 2pob and all the gear we would normally use anchor, lifejackets, flares etc..
Weight im guessing 1300kgs

Lac Leman 25degs air 20deg water calm

Both Powertech props
16 x 20
3000rpm 15.7knts 17lph just planning!
3500rpm 20knts 20lph
4000rpm 25knts 26lph
4500rpm 28knts 30lph
5000rpm 31knts 36lph
6150wot 39knts 59lph

16 x 22
3000rpm 20knts 20lph
3500rpm 25knts 27lph
4000rpm 30knts 33lph
4500rpm 32.5knts 40lph
5000rpm 37knts 50lph
5400wot 40.2knts 57lph

Three things spring to mind from this experiment.

It seems obvious but the speed of the boat almost exactly correlates to the fuel burn. I thought it would relate more to what rpm the engine was doing.

2inch pitch change had a huge loss of 700rpm at WOT

Choosing a propeller is hard ! Im tempted to run the bigger one as the engine is maybe working harder but with less revs. In the cruise zone 20to30knts you have a quieter boat and your not wringing the neck of the engine all day.

I think ill switch back to the 20 when i have a boat full

Might be of interest to anyone with either a xs700 or a df200!

[JA1000]

Good stats and useful info