Anchor battles, more SPADE versus Rocna
posted by John & Phyllis Web Site
A few weeks ago, while buried in launching and commissioning “Morgan’s Cloud”, we received an e-mail from Alain Poiraud, inventor of the SPADE anchor, questioning the validity of a graph of relative anchor holding power provided by Rocna and our decision to use it in this post.
I should point out that we were posting Craig Smith’s (a principal at Rocna) comments in there entirety (as we had done some weeks before for Alain) and therefore we were not making any comment on the validity of the graph by posting it. In fact we placed the following editorial comment under it: “The chart above was adjusted by Rocna based on the original SAIL Magazine chart, which you can see on the third page of this PDF.”
Now that we have a few moments, I have had another look at the original chart from the SAIL Magazine anchor tests and the chart that Rocna derived from it. The two charts give a somewhat different overall impression, although the Rocna still just beats out the SPADE on the original, but by a narrower margin.
As I understand it, Rocna scaled the original findings in proportion to anchor weight to generate their chart. I would be the first to admit that I’m no engineer, but it seems to me that this kind of scaling of results is not really valid. For example such treatment would slaughter a fisherman type which, none the less, can be a very useful anchor in rock and kelp covered bottoms. (See this post)
When it comes to the Rocna to SPADE comparison, surely Rocna are scaling apples and oranges since the SPADE is ballasted with lead and the Rocna is not. Sure if SPADE were trying to recommending an anchor of twice the weight for the test, Rocna would have a point to question the results, but we are talking 3 pounds difference here. It would even be possible for SPADE to turn the tables on Rocna and scale the same graph by surface area and thereby come up with a completely different result.
Chart that Rocna derived from the original SAIL magazine test.
In our opinion, choosing anchors is hard enough without the manufacturers changing the results of independent studies in ways that benefit their products.
As we have said before, we have no opinion on which of these anchors is better. We gather that in some other tests the SPADE has done marginally better than the Rocna (depending on how you read the results), the opposite of the SAIL test.
Frankly we think that these small testing differences are pretty meaningless in the real world. The point is that both are fine anchors that are dramatically better than the old style anchors we were all using up until a few years ago. And, if you are still using an old style anchor, the purchase of either a Rocna or a SPADE will definitely increase your safety and enjoyment of cruising.
Labels: Anchoring
