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Old 26 January 2021, 22:30   #1
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Waves & Swell

I just recently received some figures from the Bureau of Meteorology in regard to the history of waves & off the coast where I live (Perth Western Australia)

This is to determine the number of days I could use my RIB throughout the year and maybe if I need to get a bigger boat to increase my sea time.

Does anyone have any knowledge of where I may find info as to the size of boat and the seas it can handle.

Otherwise can you advise of the size of boat you have and the maximum seas you would take it out on, at a speed of 10 knots.

The figures I am working on are Swell + Waves.
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Old 27 January 2021, 05:07   #2
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Sounds like you need some Sea time....and some "hands on experience"Too many variables for that type of question.
Experience is invaluable,and things like type of use intended ..crew size (Family?Kids?)...distances to be covered/cruising range ...local conditions like Tidal range and Races ...Sand Bars ect ...Launching/Recovery facilities...Distance from launch sites
Boat/Trailer Storage/Mooring?...Towing...Tow vehicle .ect ect ect will all help diecide your ultimate choices.
Suffice to say most people DO go UP in size after a while if they can..and for good reason

IF YOUVE DEFINITELY decided on a RIB ...and why wouldn't you!?
I'd go for the Biggest and Best you can afford MAINTAIN and run!....After all is said and done ..a lovely calm day in perfect conditions on the water with no time constraints is a pleasure in pretty much ANY size RIB ....
YOU can't always say the same if you want to "stretch your legs" (especially in the company of larger/faster Boats) or when it Blows up Rough along way from home...more so if it's filled to capacity!
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Old 27 January 2021, 05:33   #3
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Size is too simple a question. Plenty of fun to be had by a skilled user with a jetski in huge waves. Plenty of terror to be had in a 15m boat that's badly operated or was designed for use in flat lakes not big seas.

Its frequently suggested here you'll give up long before the boat. So its not just about length - the engine, the seating the degree of shelter from weather all play a part.

However I realise that's probably not that helpful - you are trying to do a quick calculation to see if doubling the size of your boat would double the number of days you can go out...

You should be able to find the EU RCD requirements online easily enough. These split boats into 4 categories. From 50cm waves to ocean-going. Will give you a rough idea. You'll see its not a quick length decision. The RCD is far from perfect but it might give you a guide...

Quote:
Suffice to say most people DO go UP in size after a while if they can..and for good reason
Although I do find it interesting when people downsize they so often post "I forgot how much fun you could have in a small boat"... Perhaps rather than saying - could I go out in these big waves the question changes to - where can I tow my boat that would offer more shelter.
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Old 27 January 2021, 05:56   #4
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As the others have said, itís not just about size, although it can help. A well founded/engined/handled smaller boat will perform ďbetterĒ (itís all relative), than a badly handled, underpowered, inappropriate (for the conditions) larger hull.
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Old 27 January 2021, 11:15   #5
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I'm aware that swell is just a big wave but I'd separate waves and swell in your thinking. Consider swell to be very long wave length and underlying the waves. Pretty much any personal sized rib will be fine on swell since the wavelength is so long, the only requirement is to have ample power because you can be climbing a fair sized hill up the face of swell - but you get to rush down the back of it too!

The issue is more about the wave size a particular length of boat can handle comfortably, safely and unfrighteningly (new word!). It gets kinda tricky when the wavelength is similar to the length of your boat. Wave shape is also important but is variable in different conditions. Because wave shape is variable it's important to have a hull/tube shape capable of handling a variety of wave shapes.

It's all very tricky to predict.
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Old 27 January 2021, 21:26   #6
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I had owned boats and worked on boats in the UK for well over 20 years before I moved to Aus 30 years ago. One of my first jobs was from Hillarys boat harbour on a sharking boat working 30+ miles offshore. This was certainly an eye opener to big sea conditions, first day was in 5m swell on light 10-15kt wind chop. In the Uk the seas were mostly from sea chop created from wind and rarely large ocean swells like here. My first day was considered a good day out there!!!!

In saying that those seas weren't anywhere near as bad inshore. I was a volunteer with marine rescue out of Coogee for a while where most of the conditions we patrolled in on the weekends was more than capable for the average 5m boat. Just head down around the big boat ramp areas and take a look at the size of some of those smaller boats that head offshore. By checking these boat ramp areas on different days of wind and sea conditions you will soon get an idea what others are using around there. Keep in mind you don't have to head offshore is the conditions are bad as there are sheltered waters to enjoy too. Small to media ribs are common for running over to Rotnest island, which funny enough was where most of our rescues needed up being around!!!!..mostly tows from battery issues.

In terms of ribs in tough sea conditions, well just like others have mentioned personal hours at sea are vital if heading out when things aren't so good. The great thing about ribs (as long as they are in good condition) is they are incredibly forgiving compared to a tinny or glass boat of the same size. Im often out in ribs of 5m that boats of 15m aren't out in. Ive done rescues with my own boat that the size, weight and fast manoeuvrebility lets me work in conditions bigger boats can't.

Big seas close together from wind action is the worst for me now living on the far south NSW coast but large swells actually help reduce those.

In this image bellow we are fishing close to an offshore island with no wind and just ocean swell, the rib eats up these conditions. Picture taken by a fishing buddy from the water police.

I regularly ran that rib over 100k offshore chasing bluefin. My daughter now has the 5m version which is also used for offshore fishing, in saying that she's only 20yr old but has had a lifetime of boating and is qualified to skipper commercial boats anywhere in Australian waters to 80m.
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Old 28 January 2021, 03:26   #7
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Design of the hull,weight of the boat, power as others have said, will all contribute to how well the boat will handle.

So competent helm plays a strong factor as well

Having said all that I found that sub 6 metre ribs need more skill in choppy conditions than a similar hull in a 6meter plus variant ie the over 6 meter rib is more forgiving

But itís too general when you get to different manufacturers

IMHO a determination on size will only help narrow a search you may well then find your perfect rib is actually different.

A good example would be a Ribcraft 585 will outperform many plus 6 meter ribs of other brands
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Old 07 February 2021, 00:41   #8
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As others have suggested, every boat and every crew has their own "comfort" level, and normally much lower than the boat can handle. Here on the east coast of Oz 2.5 hrs north of Sydney. Zodiac 12 man (5.2 m), very capable boat but captain and crew (wife) cautious. opposite end of the scale to JohnP who really shows what can be done safely if you are experienced.

Generally, head offshore to nearby islands for fishing, 2-3 km offshore, up to 10 km along coast. Sometimes 10 km offshore during whale migration.

Rule for thumb we use: a happy trip is 2m combined swell and wave/windchop at departure. Higher swell with negligible wave/wind, not a concern, whilst rare can be "fun". Negligible swell + nasty windchop/waves (short), can be much more unpleasant. Prefer wind speed not over 20-25km. Overall tend to look at wave conditions / wind not swell (within reason)

We can spend a few hours sheltered behind an island and return home in worsened conditions and get slightly wet and still confident (40km wind and 50% increase in sea conditions).

Have been doing this here for 4 yrs with outings each week on average and have always been confident during the return trip. Not afraid to change our mind on the way out if not sure of conditions were, they to deteriorate, better safe than sorry.

With a bigger rib or more experienced crew/captain, much more aggressive conditions would be ok.

As an ex pom, note that sea conditions/behaviour are very different here to UK even if the basic physics is the same. Perhaps due to our greater exposure to wide open oceans without interruption for 1000ís of KMís

NB: Hi to JohnP. Follow your ventures with interest due to similar size zodiac and value your posts!
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Old 07 February 2021, 06:54   #9
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I think one of the biggest consideration regarding waves and swell has to be getting the boat launched and recovered. In 50 years I've never felt "near the limit" in open water but I've had a few pretty hairy recoveries when it's blown up while we've been out and getting a boat back onto a trailer with large waves crashing onto the slip wasn't fun. In that scenario the bigger and heavier the boat, the worse it is with no hope of constraining it manually.

Having a "Plan B" will be of more value than any particular size of boat.
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Old 07 February 2021, 16:48   #10
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Originally Posted by Last Tango View Post
I think one of the biggest consideration regarding waves and swell has to be getting the boat launched and recovered. In 50 years I've never felt "near the limit" in open water but I've had a few pretty hairy recoveries when it's blown up while we've been out and getting a boat back onto a trailer with large waves crashing onto the slip wasn't fun. In that scenario the bigger and heavier the boat, the worse it is with no hope of constraining it manually.

Having a "Plan B" will be of more value than any particular size of boat.

Agree with you LT. We punctured bow tube with trailer recovering in big swell
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Old 13 February 2021, 04:30   #11
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Clearly, and has been said, experience is everything because your boat may be prepared but is the skipper and are the passengers?! They often run out of inclination well before the boat runs out of capability!

Having said that, I judge things based on the meteorologists projections of Significant Wave Height (SWH) because these give you a good sense of the scale of the seas youíll be in and makes you aware that statistically 1 in 100 waves will be 1.5x SWH and 1 in 1000 will be 1.75x... Given the number of waves you will encounter during your boating this means you need to be comfortable with the prospect of meeting a wave of 1.5x the SWH you go out in because it *will* happen some day. So projections for 2-3m SWH will require you to be happy to encounter a ~4.5m wave which is pretty big!

You need to plan for a boat that will not be overwhelmed by that - and many people use the rule of thumb that concern only starts when the wave height starts to get towards 50% of boat length - but then, in the example above, I doubt youíre considering buying a 9m RIB so you would probably be happy with a 5.5-7m RIB for SWHs of 2-4m but would need to be alert for that 1 in 100, 4.5m wave.

The other factor, as has been said, is that comfort is very much about wavelength and frequency. Progress is slow and tiring if there is a step 2m chop with a 5-8s frequency or confused seas (from currents/over falls etc) to navigate through. You will likely have to back off to avoid jumping off the tops and slamming repeatedly and then youíll be juggling a planing hull at slow speeds. Itís tiring, takes concentration and is uncomfortable for passengers. It also places a significant level of strain on internal fixtures - Iíve done 60nm voyages in chop like this and found a number of screws around the console had loosened and needed a re-tighten before returning. Not a problem but something to be aware of!

So, in short, I would urge you to look up SWH predictions or live data from weather buoys in the waters youíre going out in, then try to get some real world experience of those conditions to compare your take to the data. Then you will have a good sense of what you and your passengers find acceptable.

Have fun!
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Old 16 February 2021, 03:59   #12
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Thank you for your answers.
Nobody told me what I wanted to know, but they compensated by telling me what I already knew. Evens it out I guess.

The Australian state government of New South Wales has released information on how different size waves effects different length boats. So, I now have the information that I wanted.

Unfortunately they did not provide info in regard to wave period, ie the frequency of waves, but enough for me to work on.
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Old 16 February 2021, 04:53   #13
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Quote:
Originally Posted by salty pete View Post
thank you for your answers.
Nobody told me what i wanted to hear, but they compensated by answering the actual question. Evens it out i guess.

The australian state government of new south wales has released information on how different size waves effects different length boats assuming a competent helmsman. So, i now have the information that i wanted, i just need the skills

unfortunately they did not provide info in regard to wave period, ie the frequency of waves, probably because it's to big a variable to calculate, but enough for me to work on.

thanks to everyone who took the time & trouble to reply, i knew there wouldn't be a definitive answer, but sharing your wisdom & experience has helped me make informed decisions.
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Old 16 February 2021, 05:31   #14
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Old 16 February 2021, 05:51   #15
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Lol thank you and good bye
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Old 16 February 2021, 06:02   #16
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Originally Posted by Salty Pete View Post



The Australian state government of New South Wales has released information on how different size waves effects different length boats. So, I now have the information that I wanted.


Would you be able to share this information so that we can all benefit from this new found insight?
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Old 16 February 2021, 07:38   #17
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great pic



Quote:
Originally Posted by jonp View Post
I had owned boats and worked on boats in the UK for well over 20 years before I moved to Aus 30 years ago. One of my first jobs was from Hillarys boat harbour on a sharking boat working 30+ miles offshore. This was certainly an eye opener to big sea conditions, first day was in 5m swell on light 10-15kt wind chop. In the Uk the seas were mostly from sea chop created from wind and rarely large ocean swells like here. My first day was considered a good day out there!!!!

In saying that those seas weren't anywhere near as bad inshore. I was a volunteer with marine rescue out of Coogee for a while where most of the conditions we patrolled in on the weekends was more than capable for the average 5m boat. Just head down around the big boat ramp areas and take a look at the size of some of those smaller boats that head offshore. By checking these boat ramp areas on different days of wind and sea conditions you will soon get an idea what others are using around there. Keep in mind you don't have to head offshore is the conditions are bad as there are sheltered waters to enjoy too. Small to media ribs are common for running over to Rotnest island, which funny enough was where most of our rescues needed up being around!!!!..mostly tows from battery issues.

In terms of ribs in tough sea conditions, well just like others have mentioned personal hours at sea are vital if heading out when things aren't so good. The great thing about ribs (as long as they are in good condition) is they are incredibly forgiving compared to a tinny or glass boat of the same size. Im often out in ribs of 5m that boats of 15m aren't out in. Ive done rescues with my own boat that the size, weight and fast manoeuvrebility lets me work in conditions bigger boats can't.

Big seas close together from wind action is the worst for me now living on the far south NSW coast but large swells actually help reduce those.

In this image bellow we are fishing close to an offshore island with no wind and just ocean swell, the rib eats up these conditions. Picture taken by a fishing buddy from the water police.

I regularly ran that rib over 100k offshore chasing bluefin. My daughter now has the 5m version which is also used for offshore fishing, in saying that she's only 20yr old but has had a lifetime of boating and is qualified to skipper commercial boats anywhere in Australian waters to 80m.
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