Speed topic

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DimitrisK
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KAYAK: Sit-on-top 3m polyethylene
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Speed topic

Postby DimitrisK » Fri Aug 11, 2017 8:41 pm

Hello to all,

For many years I paddle my 3m polyethylene sit-on-top kayak and I am seeking to purchase a new sit-in in order to make trips to close islands. With sit-on-top I can have a speed not bad, it is 5.8 - 6km/h stable for hours. The only issue I face is the waves and of course with short storage. With long sit-in I would experience faster trips, but I read specs speaking about 3,5-4 knots, which is about 6,5km - 7,5km /h. Not more. I am confused then, it will be a very short improvement. I would spend money only for a big improvement, let's say over 7,5km/h or even more. At the same time I need something that will be stable. I want to be safe in the open sea and not take risks and also enjoy taking photos on the go.
Do you think that specs are correct or just conservative? How about your own speed? Do you reach stable 7,5-8 km/h or more with a stable 5m kayak?

Many thanks
Dimitris

DimitrisK
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Re: Speed topic

Postby DimitrisK » Fri Aug 11, 2017 8:44 pm

In brief, in terms of speed, is it worth to spend money on a 5m cruise (not unstable race one) sit-in since I already own speeds of 6km/h with a sit-on-top that never turns upside down?

Boatsie
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Re: Speed topic

Postby Boatsie » Sat Aug 12, 2017 3:34 am

Drag, wave length, stability, volume.
My shorter kayak is easier to maintain a cruising pace then my 5 m kayaks and it is roomier. I love it heaps yet my friend that gave it to me and I were chatting the other day. I mentioned the boat and prompted the question to him, ' look, I love the boat heaps, I still have the other boat we swapped with (10 footer) and the boat you gave me is heaps better plus although the paddle is ship loads better than the expensive one I bought, it still yours plus the skirt is top shelf. My new one's being built soon. '
He replied, ' full of holes, '
We both laughed,' yeah, I lost count at 8 but I'll see ya Sunday. There is epoxy and 3 inch glass ready on desk, she's in shed, dry and hard as rock. '
Suits us.
In terms of speed, wave length of displacement and frictional drag will greatly influence effort required to get speeds. If you can try one out. I'm glad I used the holy boat because it surprised me as to how fast a 55 year old boat is. I hope I get to keep it :P
Best of luck brother

Boatsie
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Re: Speed topic

Postby Boatsie » Sat Aug 12, 2017 3:43 am

As per own speed.
When playing on flat water with a dolphin, a engine repair speed boat and me in my otium winner (5m), we were travelling same pace for about 250 metres , the speed boat skipper yelled we were doing 10knots. I had my own decent bow wave.
Doubt has me now, maybe he yelled 10clicks. (Used to nautical chat).
Hence flat out, not long, I top out at 10 something or other.
Takes me all the best part of the day to do 14 km in my 10 footer. Twice as quick while towing my mate a lot in my 5 m. Same route. Similar tide.
Wish you well

Camanche73
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Re: Speed topic

Postby Camanche73 » Sat Aug 12, 2017 8:51 am

Dimitris, even based on your conservative estimate of increase from 6km/h to 7.5km/h, that's a 25% increase. Pretty large increase in most people's minds.
It's not necessarily about top speed, but how easily you can maintain that speed over distance and in different conditions.
A lot of other factors, but most SOT I have seen are wide and hard to promote a good forward stroke.
Length is only one element in the equation, but only you can decide wether it is worth the outlay for a different boat or not.

mattsema4
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Re: Speed topic

Postby mattsema4 » Sat Aug 12, 2017 11:53 am

Speed has been covered previously on the forum and general consensus is that most kayaks will cruise somewhere in the 6-8 kilometre per hour.
There is a formula that will predict terminal hull speed and generally longer equals faster.
Interesting to look at Expedition Kayaks blog and their Audax. Average speed over a set course was over 10 Km per hour.
My Epic 18 easily cruises in excess of 8 Km per hour. The ability to carry gear and maintain speed over distance is what you get with your dollar. I know what I prefer to paddle

Boatsie
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Re: Speed topic

Postby Boatsie » Sat Aug 12, 2017 6:20 pm

Displacement speed formula from internet. Somewhere.
"As a very general rule the maximum speed of any displacement hull--commonly called its hull speed--is governed by a simple formula: hull speed in knots equals 1.34 times the square root of the waterline length in feet (HS = 1.34 x √LWL)."

Terminal speed is faster yet loss of buoyancy and gain of drag greatly increases effort to paddle beyond displacement speed. Semi planing hulls which most kayaks are use ocean swells etc to gain power and travel above displacement without too much effort for fast pace.
Not always true.. Maybe I'm weak; my shorter kayak cruises faster than my longer kayaks. Could be it's light weight low drag and my cruise speed being lots lower than 5 knot or whatever 5m equates as.
Best to take it for a spin, if it's comfortable less effort might be wasted.

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NorthSIKer
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Re: Speed topic

Postby NorthSIKer » Sat Aug 12, 2017 7:54 pm

I'm actually stunned that you can maintain 6km/hr in a 3m poly sit on top!

Top speed is so much the issue as paddling efficiency. I don't generally average more than 6-7km per hour (unless under a following sea) on longer trips. The key to me is not being too worn out at the end of the day so I am comfortable to get up the next day and do another 40km or more. I would work a whole lot harder to average 7-8km per hour.

I have paddled out with a number of people quoting steady cruise of 10km-ish in their boats but after 5 or 10km on the sea they are falling behind my steady 6-7km.

You will see a whole lot of references to boats average 10km/hr etc. Yes, they can be real recordings but often by very good paddlers or shorter distances. Over long distance multi-day trips, 6-8km hr average would be pretty standard over the mix of conditions (without sail), even for good paddlers. I would love to know the average moving time speeds recorded over the whole trips for those that have circumnavigated Australia (Freya, Stuart, etc).

Anyway, in addition to the above (noting others will raise a whole range of (correct) qualifications) basically longer (to a point as longer hulls can be more work at slow speeds), skinnier (provided you are not fighting to keep upright) and stiffer boat will be more efficient to paddle.


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