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Riptide performance - build tweaks

Posted: Sat October 23rd, 2010, 4:19 am
by Kevan
Hello all!
A few questions if I may. I have purchased MG’s Riptide drawings and am preparing detailed drawings to help through construction and planning (materials and costing). Having finished the basic drawings I checked the hydrostatics to see if it was as good a design thought. For a small cruiser the numbers work out really well actually – hats off to Mr. Griffiths!

I would like to finish off the design but before I progress, I thought I should get some “hands on” feedback. For example the rudder can be tweaked if it doesn't perform well. The brace under the mast is not detailed well - should it be stronger? I can easily design that now but retrofitting later . . .

Here goes - Feel free to pitch in, even to comment that the answer to the question is immaterial or to highlight questions I haven’t asked that you think are important.

- Is the Riptide as designed, “balanced”? What would you change?
- Is the rudder balanced or should the centre of rotation be shifted?
- Is it stiff, as predicted? Is there a shoulder? At about what heel?
- Is the stock sail arrangement suitable (too small, always reefed?)
- Does it sail well???? (Should I build it? Four years of my life for a poor sailing boat is too sad to contemplate!!)
- Biggest of all, would you change anything in the design?
- Should I make it a double chine design? (Big change, please say "No")

I am sure more questions will arise. I will post them as they occur. Thanks in advance.

Re: Riptide performance - build tweaks

Posted: Wed October 27th, 2010, 11:18 pm
by JamesH
Hihave you considered the bilge keels mods that Richard Hare gives in PBO several years back?
Would make the keels more hydro dynamically satisfactory.
Sail area can easily be added.
Do you realise there is a grp golden hind part finished on ebay at the moment.
Or perhaps you relish the thought of building as much as sailing as I do! Ra my hands across some marine ply in selco the other day -lovely!!
Yours James

http://WWW.WW for me!!!

Re: Riptide performance - build tweaks

Posted: Sat October 30th, 2010, 10:31 am
by Kevan
Thanks for the comment. I hadn't thought about the bilge keels, they seemed so simple, how could the be tweaked?!?

I have had a quick search for Richard Hare/PBO/Bilge with little success. Any hints as to where I could find it?

You're building a Waterwitch, yes? Proceeding well?

If you're interested, here is a snapshot from the Free!ship analysis I undertook on the Riptide - slightly modified to have a longer LWL to increase the fineness of the entry.
Riptide Lines Plan from Free!Ship modelling
Riptide Lines Plan from Free!Ship modelling
ym_riptide_31 -Freeship linesplan.jpg (235.24 KiB) Viewed 12754 times

Cheers all and remember, any input welcome.

Re: Riptide performance - build tweaks

Posted: Mon November 1st, 2010, 10:58 pm
by JamesH
Vibration I believe at about 6knots, will find the Practical Boat owner in question and scan the pages.
Have yet to build the ww have Keel, all frames and started on the deck beams.
Yours James

Re: Riptide performance - build tweaks

Posted: Wed November 10th, 2010, 3:12 am
by Kevan
Pretty quiet! I can only assume that she is "perfect as designed".

Seriously though, I know there are few Riptide owners and they may not have read the posting - although any comments from the YM plywood single chine boats would be welcome.

I will however push on with the final design drawings with a few enhancements of my own including James comments on the bilge keel vibration. I have been looking at the Golden Hind (a similar size and shape hull but slightly larger radius shape to the hull profile) for hints and will shorten the keel shape similar to that shown on the link that James posted in the GH forum (see also Chuck Paine's changes to his "Annie" - see, another ripper ship).

I will also:
- Add a short bowsprit (or at least reinforce so that it can be added with impunity later on)
- Reinforce the deck and chain plate area fore and aft of the mast so that I can shift it if necessary to improve the performance without a rebuild
- and after much consideration (actually, still undecided), GRP cover the exterior of the hull. It will mean building it upside down and turning it over, but that should also make attaching the ply easier.

Re: Riptide performance - build tweaks

Posted: Wed November 10th, 2010, 5:24 pm
by JamesH
Found the article pbo March 09 will scan when I get home tonight yours James

Re: Riptide performance - build tweaks

Posted: Fri November 19th, 2010, 6:08 pm
by Fiddler's Green
Re the balanced query, that refers to the sail plan balancing the keel shape for helm weight. What you need to achieve is slight weather helm. too much helm slows the boat and is tiring on the crew, cured by adding sail area forward or keel area aft. the keel on the riptide is OK, and no one has complained of excessive helm.

As for balancing the rudder, a 5% of area in front of the pivot is considered the maximum, I have none to speak of on mine on an Eventide and the helm is light under sail, a little heavier under power. That is when a semi balanced rudder comes into it's own.

Re the bilge keels, I honestly think Richard Hare is making too much of it. If you are trying to make the boat more effieient, or If you want to have a racing machine you have the wrong boat. My bilge keels gently 'thrum' at 5 knots, very satifying to know we are sailing well and it does not annoy me.

Mak Urry, the GH builder, makes a very good point though, 'would an owner be happy to throw 350lb of ballast over the side?' Without those keels the GH would not get it's 'Ocean'' clasification either!

Suck it and see, you can always add a hydrodynamiclly shaped wooden plate to the inside of the keel later if it troubles you! some Eventide owners with light keels added shaped steel plates to the inside faces of the keels to put weight and shape in the right place. that works too.

Hope that helps