Reply
 
Thread Tools Search this Thread
 
Old 01 November 2015, 10:18   #91
Member
 
dubrus's Avatar
 
Country: UK - Scotland
Town: Glasgow
Make: Ribcraft 6.8
Length: 6m +
Engine: Suzuki df200
Join Date: Jun 2010
Posts: 2,085
I have never tried I don't think, the 551 normally has that info.
__________________

__________________
dubrus is offline   Reply With Quote
Old 01 November 2015, 16:18   #92
RIBnet supporter
 
jepho's Avatar
 
Country: UK - England
Town: Leighton Buzzard
Boat name: no boat yet
Make: no boat yet
Length: no boat
Engine: no boat yet
Join Date: Oct 2015
Posts: 75
Quote:
Originally Posted by Last Tango View Post
You're over thinking this one.
All the maths in the world will only give you a headache and get you "fairly close".
Trial and error is what gets you spot on and it's likely, if you buy a second-hand boat, someone will have already fitted the best prop. If not, cheat...... just stick the question on here and someone will already have done the work for you.
You're generally looking for the engine to be reaching it's optimum max revs at full throttle with your normal load (varies but generally between 5000 & 6000 rpm) and there's a bit of scope there.
Replacing a prop takes about 10 minutes. Huge variance in price, you'll see them on ebay, but the last three second-hand stainless props have cost me between 130 & 150.
You'll find endless debate about the subject on here, all relevant, but don't get hung up on it, it's not a deal breaker. More important is, if the prop is damaged make sure there isn't other damage round the area.
Thanks, Last Tango. I can identify with the advice to cheat. No point in reinventing the wheel. I appreciate the more detailed explanation too.
__________________

__________________
jepho is offline   Reply With Quote
Old 01 November 2015, 16:52   #93
RIBnet admin team
 
Poly's Avatar
 
Country: UK - Scotland
Boat name: imposter
Make: FunYak
Length: 3m +
Engine: 2 stroke YAM 20 HP
MMSI: 235089819
Join Date: Sep 2005
Posts: 10,112
Just catching up on this...

I think Dubrus' approach of putting boats into categories is probably fair enough. I'm not sure I agree with his definition though by hull "v" there are boats in his second group I am sure are comparable to those in the first. I'd also suggest the differentiator is not the angle of Hull or absence of planing pad, but the build quality and fit out; the split between the categories is therefore fairly arbitrary and will change with age.

In terms of tube material there are three to pick from. hypalon is by far the most popular here, and Beware some cunning pvc marketing that uses similar sounding names like hypatex! in your budget I would avoid PVC as an older pvc boat may be closer to needing an expensive retube. polyurethane is not discussed much on the forum, it isn't significantly cheaper and so is usually ignored in these parts (and is harder to repair) but those who have such tubes that I have spoken to have generally been pleasantly surprised.
__________________
Poly is offline   Reply With Quote
Old 01 November 2015, 17:33   #94
RIBnet supporter
 
jepho's Avatar
 
Country: UK - England
Town: Leighton Buzzard
Boat name: no boat yet
Make: no boat yet
Length: no boat
Engine: no boat yet
Join Date: Oct 2015
Posts: 75
Quote:
Originally Posted by Poly View Post
Just catching up on this...

I think Dubrus' approach of putting boats into categories is probably fair enough. I'm not sure I agree with his definition though by hull "v" there are boats in his second group I am sure are comparable to those in the first. I'd also suggest the differentiator is not the angle of Hull or absence of planing pad, but the build quality and fit out; the split between the categories is therefore fairly arbitrary and will change with age.
Thank you, Poly. I will bear that in mind.

Quote:
Originally Posted by Poly View Post
In terms of tube material there are three to pick from. hypalon is by far the most popular here, and Beware some cunning pvc marketing that uses similar sounding names like hypatex! in your budget I would avoid PVC as an older pvc boat may be closer to needing an expensive retube. polyurethane is not discussed much on the forum, it isn't significantly cheaper and so is usually ignored in these parts (and is harder to repair) but those who have such tubes that I have spoken to have generally been pleasantly surprised.
OK. I will look for Hypalon as the tube material.
__________________
jepho is offline   Reply With Quote
Old 02 November 2015, 13:26   #95
Member
 
tony t's Avatar
 
Country: UK - Wales
Town: west mids /tywyn
Boat name: HAWK
Make: RIBCRAFT/ Suzuki 250
Length: 7m +
Engine: Tohatsu 3.8/15hpsuzi
MMSI: 235086594
Join Date: Apr 2008
Posts: 4,284
Quote:
Originally Posted by jepho View Post
Thank you Jeff. Lots of good information and ideas here. I have had a drive of a Humber with twin 60s. It was a 5.85 I think. Not madly fast but very stable in rough seas and highly manoeuvrable. An impressive craft when pressed hard.



I saw a really beautifully kept RIB which was adorned with four (what I had taken to be) shock mitigation seats, in Portsmouth very recently. They looked so very expensive and I did not dare to ask the price. All had an adjustable suspension unit under the seat which appeared to be sitting atop an adjustable double cantilever type arrangement. Here are some pix.

No wonder you like it .... It's a Ribquest


Sent from my iPhone using RIB Net
__________________
When you get to the end of your rope..tie a knot and hang on..!!
Aberdovey Ribs
B.I.O.C.Member
B.S. LEADER
tony t is offline   Reply With Quote
Old 03 November 2015, 03:48   #96
Member
 
Country: UK - Scotland
Boat name: Wildheart
Make: Humber/Delta Seasafe
Length: 5m +
Engine: Merc 60 Clamshell
MMSI: 235068449
Join Date: Apr 2007
Posts: 4,610
Quote:
Originally Posted by Poly View Post
Changing from single to twins isn't trivial and the benefits may be less than you expect. Not all transoms would take the weight or power of two big engines either.

Quote:
Originally Posted by ShinyShoe View Post
TwinsAs Poly said twins is not the sensible option. 2 x70HP would give you power something like 100HP...
<snip>
..... If an engine fails you either have a 6HP spare to deploy or you chuck out the anchor and hope some nice passing boat gives you a tow.

Jepho, Hi, Welcome to ribnet!

There is a lot of banter around single vs twins. I'll summarise here by saying what is maybe true with twin 150s vs a 300 is not necessarily true lower down the scale. Poly's comment on changing from singe to twins is spot on - as you will need to rebuild the transom. Twins to singe usually involves removing wood.

Do a search for twin - single and filter for me in the user box - I have expanded on these misconseptions numerous times, but in summary:

Weight
- at the bigger engines due to the lower sales volumes more share the same hardware so quite often a 150 will be not too far off the weight of a 300. Down at the "100 or so" mark quite often twins can weigh less than a single + aux. Search my other posts for some real life examples.

Twin everything
- Most older engines once running are entirely self sufficent. Also most new engines with a tiller option likewise - others you'll need to check, E.g my (admittedlty very old) clamshell I could disconnect the battetry and it would still run. Plenty of threads on here about emergency pull starting.....

"Double drag".
- nope. The drag is approx related to the frontal area cubed & the speed squared. smaller engines have smaller gearboxes, and the smaller the boat the less the top speed is likely to be, and as most on here regardless of boat or engine size reckon about 1l/nautical mile at 20-25 knots cruising speed..... (look for the fuel economy threads)


Quote:
Originally Posted by jepho View Post
Thanks Poly. Is there a particular type of transom I would need to ensure was in the specification? I have no idea what to ask for. Will it be obvious which hulls would permit two engines?

Please forgive the dumb questions.
There is no such thing as a dumb question.... someone will always know more on a subject. you may be answering smeone else's Q next time.

Transoms these days are usually rated for a weight and a HP. Some show a separate set of numbers for twins. Simple rule - don't exceed those numbers!

Re. the transom for twins - most transoms will need a "well" cut in for a single. This is because there is less transom depth the further from the centreline ine you go so the prop then hangs below it and so don't need to cut the transom. I seriously looked at twin 30s for mine, as I had a helathy 30 from my previous SR4 but as the Humber's transom was cut the woodwork was going to be way too much hassle so I got a single 60 instesad.

Also re,. the "underpowered" thing - most on here would say "go as big as you can" - to which I agree, BUT if your budget doesn't allow then "underpowered" isn't the end of the world.
E.G. most here would say "get a 50 - absolute minmum a 40" for a 4m Searider......errrr I ran one with a 25Hp for 3 years, and it crusied at 20 knots quite happily. Ok, took a few seconds to get up on the plane as opposed to "instant", but unless you are stop - start rescue boat type work is that really an issue? - Upgrading to a bigger engine later is always an option.


Another thing to think of - as we have all done you buy what you think is the baot you want...until you use it and realise that actually this would have been bettrr if... and that isn't really needed for my use..... type thing. Chances are you will be changing for something new (to you!) in a few years anyway.


Whatever happens there will be plenty of opinion to weigh up on here! ....and whahtever happens - your choice will suit your way of working / budget / travel / etc.
__________________
9D280 is offline   Reply With Quote
Old 03 November 2015, 18:20   #97
RIBnet supporter
 
jepho's Avatar
 
Country: UK - England
Town: Leighton Buzzard
Boat name: no boat yet
Make: no boat yet
Length: no boat
Engine: no boat yet
Join Date: Oct 2015
Posts: 75
Quote:
Originally Posted by tony t View Post
No wonder you like it .... It's a Ribquest


Sent from my iPhone using RIB Net

Yes, I had to say that it was very beautiful. Ribquest you say...? Premium product just by appearance any way. I am going to have to work much harder and that was not in my retirement plan.
__________________
jepho is offline   Reply With Quote
Old 03 November 2015, 18:32   #98
RIBnet supporter
 
jepho's Avatar
 
Country: UK - England
Town: Leighton Buzzard
Boat name: no boat yet
Make: no boat yet
Length: no boat
Engine: no boat yet
Join Date: Oct 2015
Posts: 75
Quote:
Originally Posted by 9D280 View Post
Jepho, Hi, Welcome to ribnet!
Hi 9D280. Thanks for the welcome.

Quote:
Originally Posted by 9D280 View Post
There is a lot of banter around single vs twins. I'll summarise here by saying what is maybe true with twin 150s vs a 300 is not necessarily true lower down the scale. Poly's comment on changing from singe to twins is spot on - as you will need to rebuild the transom. Twins to singe usually involves removing wood.

Do a search for twin - single and filter for me in the user box - I have expanded on these misconseptions numerous times, but in summary:

Weight
- at the bigger engines due to the lower sales volumes more share the same hardware so quite often a 150 will be not too far off the weight of a 300. Down at the "100 or so" mark quite often twins can weigh less than a single + aux. Search my other posts for some real life examples.
OK. Understood.

Quote:
Originally Posted by 9D280 View Post
Twin everything
- Most older engines once running are entirely self sufficent. Also most new engines with a tiller option likewise - others you'll need to check, E.g my (admittedlty very old) clamshell I could disconnect the battetry and it would still run. Plenty of threads on here about emergency pull starting.....

"Double drag".
- nope. The drag is approx related to the frontal area cubed & the speed squared. smaller engines have smaller gearboxes, and the smaller the boat the less the top speed is likely to be, and as most on here regardless of boat or engine size reckon about 1l/nautical mile at 20-25 knots cruising speed..... (look for the fuel economy threads)
I see...

Quote:
Originally Posted by 9D280 View Post
There is no such thing as a dumb question.... someone will always know more on a subject. you may be answering smeone else's Q next time.

Transoms these days are usually rated for a weight and a HP. Some show a separate set of numbers for twins. Simple rule - don't exceed those numbers!

Re. the transom for twins - most transoms will need a "well" cut in for a single. This is because there is less transom depth the further from the centreline ine you go so the prop then hangs below it and so don't need to cut the transom. I seriously looked at twin 30s for mine, as I had a helathy 30 from my previous SR4 but as the Humber's transom was cut the woodwork was going to be way too much hassle so I got a single 60 instesad.

Also re,. the "underpowered" thing - most on here would say "go as big as you can" - to which I agree, BUT if your budget doesn't allow then "underpowered" isn't the end of the world.
E.G. most here would say "get a 50 - absolute minmum a 40" for a 4m Searider......errrr I ran one with a 25Hp for 3 years, and it crusied at 20 knots quite happily. Ok, took a few seconds to get up on the plane as opposed to "instant", but unless you are stop - start rescue boat type work is that really an issue? - Upgrading to a bigger engine later is always an option.
Thanks for this... most helpful.

Quote:
Originally Posted by 9D280 View Post
Another thing to think of - as we have all done you buy what you think is the baot you want...until you use it and realise that actually this would have been bettrr if... and that isn't really needed for my use..... type thing. Chances are you will be changing for something new (to you!) in a few years anyway.


Whatever happens there will be plenty of opinion to weigh up on here! ....and whahtever happens - your choice will suit your way of working / budget / travel / etc.
I am obliged to you for a very helpful post.
__________________

__________________
jepho is offline   Reply With Quote
Reply

Tags
rib

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 04:39.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.