PredictWind

[Vincent]

I am planning a trip to Maine and downloaded PredictWind to play around with their weather routing. I have a CD33. The nearest design that I see in their list of boats might be the Alberg 35. Are there any CD33 owners using PW, and what are you using for your boat polars?

[Paul D.]

You could see if these are listed and can probably go somewhere between a CD30 and CD36 if you like. But I reckon an Alberg 35 may be close enough.

[Steve Laume]

Predict Wind does not list a CD30 either. I had a good friend feed me weather information on my passages, last winter. He used a Bristol 35 and reduced it by some percentage. Raven was pretty fast with a clean bottom and fresh sails, so the speeds worked out fine. What I found disturbing was about a 10 knot discrepancy in wind speed. There is a huge difference between 30 or 35 knots predicted and 40 to 45 experienced. I have heard this from others as well so be aware that wind speeds may be higher than PW tells you.

It is still a very valuable tool for longer passages where a forecast from home will not cover the entire trip, and you are out of VHF range, Steve.

[Vincent]

Steve: Good to know about the wind speed difference between their predictions and observed. From what I can see of their boat polars, they use 15 knot wind speed, and you boat speed at 50,90, and 160 degrees. Those speeds need to be with no current plus or minus. PW has no Cape Dory polars listed. I’ll use the Alberg 35 until I can get my own data points. It’s an interesting app. Perhaps not as useful on a coastal run to Maine and back, but with an Iridium Go you can pull down info from the satellite link mid ocean. For any considering it, you pay for the Go, and both subscriptions, PW for the info and Go for the link.

[Paul D.]

I've heard the Windy app is used and liked too, but I have no experience with it.

[wikakaru]

An alternative is to use OpenCPN and intall the Polar Plugin, then download the grib files from whatever service or app you like (I use Zygrib) and use them in OpenCPN. You can create your own polar diagram from your own experience with your boat using the Edit Manual mode of the Polar Plugin.

--Jim

[Vincent]

Jim: Thanks for your reply but I have to tell you, I read that and in my mind it sounded like Charlie Browns teacher. I have no idea what you said,lol. I’ll sail the boat and try to get my own polars. Until then I’ll stick with the Alberg 35. I’ve sailed to and from Newport and the Chesapeake many times. We got the local weather and took off. This app is a good tool, I’ll use it but I’m trying it out for now.

[Steve Laume]

I really like Windy as it gives you the big picture and seems to be pretty accurate. I had no way of updating it while off shore but you can get a forecast that is accurate for a few days. I have pulled it up and then taken screen shots for a few days to see what I was getting into. The best part is that it is free.

If you are only going to be doing a 3 to 5 days crossing, shore based weather should be good enough to plan your trip, Steve.

[fmueller]

Steve,

I’ve had the basic PW package for a few years. No weather routing - which I don’t need. I’ve found if I look at the wind gust predictions and sort of split the difference with the wind map - that’s closer to how it actually feels and how much “laundry” you want hanging out. Sometimes the steady wind speed can be pretty civilized - but the gust are nasty. Happens here especially from the NW in the colder months on the backside of a front where the wind is 10-15 but it’s gusts to nearly 30. So I always look at the gust map and plan for that.

Cheers

[wikakaru]

Jim: Thanks for your reply but I have to tell you, I read that and in my mind it sounded like Charlie Browns teacher. I have no idea what you said,lol. I’ll sail the boat and try to get my own polars. Until then I’ll stick with the Alberg 35. I’ve sailed to and from Newport and the Chesapeake many times. We got the local weather and took off. This app is a good tool, I’ll use it but I’m trying it out for now.

I got a laugh out of the Charlie Brown teacher comment. Sorry, it's too easy for me to geek out sometimes. I suspect that using a close cousin's polar predictions in your current app will be good enough. The error from inaccurate weather forecasts will probably be far more significant than the differences in performance polars between your boat and the one you use in PredictWind.

Smooth sailing,

Jim

[Frenchy]

For whatever little it's worth, I found these polar diagrams for a CD 33 with a 150 Genoa. I really don't know how to
interpret all of this. Maybe someone can explain. I'll probably have to add another post as there are four pages.
Good luck in using this information as I am lost.

[Frenchy]

More Polars. These pages were given to me when I bought the boat - Jean

[Paul D.]

Wow, first time I’ve seen those! Looks about right to me though I think we have a 135% Genoa. We regularly hit 7kts boat speed in 20 knots of wind on those angles. Thanks for posting.