Hobie Cat Forums

It is currently Tue Sep 02, 2014 7:42 am

All times are UTC - 8 hours [ DST ]




Post new topic Reply to topic  [ 16 posts ]  Go to page 1, 2  Next
Author Message
PostPosted: Tue Apr 26, 2011 12:03 am 
Offline
Site Rank - Admiral

Joined: Wed Dec 10, 2008 8:53 pm
Posts: 232
Looking thru some old tracks, it seems like I typically get 50-55 degrees upwind, at this angle the max consistent speed I seem to get is somewhere around 5.5mph.

Anyone know if the boat gains speed by falling off 15 degrees or so? Any idea how much speed increase, maybe a percentage? Typical winds are 10-20mph, we generally have 1-3ft wind waves so that might be the reason for slightly less speed than others :)


Top
 Profile  
 
PostPosted: Tue Apr 26, 2011 9:37 am 
Offline
Site Admin

Joined: Tue May 27, 2003 12:44 pm
Posts: 8979
Location: Oceanside, California
Fastest sailing angle should be around 90-120 degrees off the wind.

_________________
Matt Miller
Director of Parts and Accessory Sales
Hobie Cat USA


Top
 Profile  
 
PostPosted: Tue Apr 26, 2011 9:46 am 
Offline
Site Rank - Admiral

Joined: Wed Dec 10, 2008 8:53 pm
Posts: 232
mmiller wrote:
Fastest sailing angle should be around 90-120 degrees off the wind.


Cool thanks, I also found this interesting chart for a J/80 ??? I'm not really sure what kind of boat it is or its performance, but the chart indicates something along the lines of what you suggested.

In best case scenario looks like we might get 1/2 a knot increase by falling off 10-20 degrees :mrgreen:

Image

Check Google Books Page 74 of
Getting Started in Sailboat Racing
By Adam Cort, Richard Stearns


Top
 Profile  
 
PostPosted: Wed Apr 27, 2011 5:10 am 
Offline
Site Rank - Admiral

Joined: Sun Jul 08, 2007 8:52 am
Posts: 167
Location: Boynton Beach
I my experience, If I'm moving at 5.5 to 6 knots 70-75 degrees off the wind, I'll drop to around 3.5 once inside of about 65 degrees. Most mono-hulls will point much higher than most multi-hulls.

Ted


Top
 Profile  
 
PostPosted: Wed Apr 27, 2011 7:47 pm 
Offline
Site Rank - Old Salt

Joined: Fri Dec 05, 2008 2:32 am
Posts: 1783
Location: Calga NSW, Australia
Something I have only come to realise recently, but which may have been obvious to many, is that when a boat is on a reach, the optimal angle of the sail to the wind is always the same and it is only the angle of the boat to the sail that alters:
Image
Because the sail is acting like a wing when on a reach, the "lift", or propulsive force from the wind is at 90 degrees to the sail.
As you can see from the diagram, when the boat is on a close reach, it approaches 90 degrees to the propulsive force of the sail, at which point it stops moving forward.
On the other hand, when the boat is between a beam reach and a broad reach, the hull of the boat is travelling more or less in the same direction as the propulsive force, which is why that is the fastest point of sail.
This is consistent with JollyGreen's diagram, which suggests that if the optimal angle of a sail to the wind is 45 degrees, then the fastest point of sail is at a right angle to that - 135 degrees.
I drew the above diagram, so don't assume it came from an authority on sailing.

_________________
Image


Top
 Profile  
 
PostPosted: Wed Apr 27, 2011 8:43 pm 
Offline
Site Rank - Admiral

Joined: Wed Dec 10, 2008 8:53 pm
Posts: 232
Thanks for the detailed explanation, makes sense, I usually watch the telltales and make sure they are both flowing. Based on your explanation I think I now understand why it's best that they be flowing on both sides of the sail. :)


Top
 Profile  
 
PostPosted: Thu Apr 28, 2011 2:14 am 
Offline
Site Rank - Old Salt

Joined: Wed Dec 19, 2007 4:07 am
Posts: 598
Location: Punta Gorda, FL
Yes, both telltales should always be flying, unless you're going downwind and using the wind to push against the sail rather than create lift.

Creating lift is always more powerful, which is why the really fast trimarans almost never go straight downwind. They can reach downwind faster, though the distance covered will be greater.

Here's the chart for a Multi 23. Note that the curves for each wind speed "bulge" a bit in different places, with the bulge drifting downward as wind goest up. The best angle for max speed depends on wind speed. It's more across the wind in light air, further downwind in strong winds.

Image


Top
 Profile  
 
PostPosted: Thu Apr 28, 2011 2:40 am 
Offline
Site Rank - Old Salt

Joined: Fri Dec 05, 2008 2:32 am
Posts: 1783
Location: Calga NSW, Australia
Tom Ray wrote:
The best angle for max speed depends on wind speed. It's more across the wind in light air, further downwind in strong winds.

I'm guessing that's because the stronger the wind, the faster the boat goes and the more the apparent wind shifts forward, so you end up going more across the (apparent) wind anyway.

_________________
Image


Top
 Profile  
 
PostPosted: Thu Apr 28, 2011 9:11 am 
Offline
Site Rank - Admiral

Joined: Wed Dec 10, 2008 8:53 pm
Posts: 232
Wow, how did you find that polar chart? I looked for a while trying to find one for a trimaran! Thanks for posting that! :o

Looks like we can gain somewhere between 10-40% in speed by falling off to 70 degrees, definitely will be something to play with the next time I'm out. Thanks again! :mrgreen:


Top
 Profile  
 
PostPosted: Fri Apr 29, 2011 3:47 am 
Offline
Site Rank - Old Salt

Joined: Wed Dec 19, 2007 4:07 am
Posts: 598
Location: Punta Gorda, FL
JollyGreen wrote:
Wow, how did you find that polar chart? I looked for a while trying to find one for a trimaran! Thanks for posting that! :o

Looks like we can gain somewhere between 10-40% in speed by falling off to 70 degrees, definitely will be something to play with the next time I'm out. Thanks again! :mrgreen:


I think that one came from the Multi 23 website. A friend of mine owns one, and I have raced it with him.

Remember that the AI is a very different beast from the Multi 23. While the general tendencies will be similar, don't expect that huge performance difference that a really fast tri experiences.


Top
 Profile  
 
PostPosted: Sat Apr 30, 2011 11:55 am 
Offline
Site Rank - Captain

Joined: Wed Mar 09, 2011 7:37 pm
Posts: 52
Tom, great chart for the Multi23. Multihulls definitely perform different than mono's. I crew on a Corsair 27, which can perform a "semi-planing" status. Looking at the Multi 23 numbers, it looks like it can hit about 17.5 knots. Best I have seen on my friend's Corsair is 17.4 knots at about the same angle in which the Multi23 can hit this mark. Do the Multi23s have the ability to achieve this "semi-planing" state? The Corsair, in theory, can hit higher numbers than 17.4, but I have yet to see this.

I do realize that the AI or TI, with standard gear, can not achieve a planing status.

Jolly, Tom's advice is good. I would generally steer clear of mono numbers, as compared to a multi. Here is a link to J 80 stuff http://www.jboats.com/j80/ Good solid mono racing class.

Wind permitting, when racing monohulls, we would have a tendency to point further off the VMG than the monos, and plan on the Corsair's speed to make up the difference.


Top
 Profile  
 
PostPosted: Sat Apr 30, 2011 12:58 pm 
Offline
Site Rank - Old Salt

Joined: Fri Jan 05, 2007 9:21 pm
Posts: 2229
Location: Maui, Hawaii
PeteS wrote:
I do realize that the AI or TI, with standard gear, can not achieve a planing status.
The thought is right but the statement is not correct. By my calculations an AI top speed should be about 7mph and the TI about 8mph, based on the length at the waterline. I break 10mph more often then not on an AI and 11-12mph on a TI in good winds. BUT... it mostly only happens for a few seconds now and then. Nothing you can rely on.

Once in a long while, I get the perfect large gust of wind, when I'm going in the perfect direction and already sailing pretty fast, sometimes lasting up to a minute which gives me "OH WOW!" speeds on the GPS, (Sept 22, 2007 - 19.7mph, producing large +10 foot high rooster tails from the bow of each AI).

When the AI reached planing speed, you can feel and hear a low humming. :D But, trying to plan for it or rely on it will just bring disappointment.

_________________
Image
http://KayakingBob.com - - - - - Hobie Island Sailing since 2006 - - - - - 2011 & 2012 Hobie AIs and a 2012 TI


Top
 Profile  
 
PostPosted: Tue May 03, 2011 3:06 am 
Offline
Site Rank - Old Salt

Joined: Wed Dec 19, 2007 4:07 am
Posts: 598
Location: Punta Gorda, FL
Pete, I used to own an F-27 (hull 162) and it can go almost 20 knots in flat water, faster when surfing. The previous owner surfed ours up to 25 knots, at which point his speedo pegged, but he went even faster.

Surfing is cheating, though! ;)

The fastest I ever got it going was mid-upper teens, but I had no speedo by then and would not have had time to look at it if I did!

The Multi 23 is unlike the F-27 in that it is designed to fly on one hull. That is when it hits the upper teens. The main hull with its open centerboard trunk is a huge brake, and when you lift it up into the air, the boat accelerates.


Top
 Profile  
 
PostPosted: Tue May 10, 2011 5:32 pm 
Offline
Site Rank - Captain

Joined: Wed Mar 09, 2011 7:37 pm
Posts: 52
Tom,

Nice! Multi 23 sounds similar to Seacart 30. A Multi 23 "Tri Fecta" was listed in the 2011 Conquistador Cup, but they DNF'd the race. I was looking forward to seeing one.

Certainly got a kick out of the April fools pictures for the Hobie AI hydrofoils. Had me going for about 2 minutes.


Top
 Profile  
 
PostPosted: Thu May 12, 2011 3:07 am 
Offline
Site Rank - Old Salt

Joined: Wed Dec 19, 2007 4:07 am
Posts: 598
Location: Punta Gorda, FL
PeteS wrote:
A Multi 23 "Tri Fecta" was listed in the 2011 Conquistador Cup, but they DNF'd the race.


That's the boat! I have some pictures and video of it on my website:

Multi 23 Trimaran


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 16 posts ]  Go to page 1, 2  Next

All times are UTC - 8 hours [ DST ]


Who is online

Users browsing this forum: jerinaldi and 10 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group