I understand the position you are in. There are plenty of people walking the docks that can give advice; but the bottom line is you need to base your decisions on what you KNOW to be correct. Always keep that in mind; and keep in mind that riggers are very well paid because they KNOW what the correct applications are and the decisions they make are for the safety of more people than just the owners. I'm sure that Harken's calculator is on the conservative side; but they also need to be sure that their advice is not wrong in a large percentage of the inquiries.
Most people that own a boat; specifically a sailboat are aware that the safety of the crew and guests are ultimately the responsibility of the skipper; so when something that could have been prevented happens the liability rests with the skipper (owner) in your case; not the people who may have given their (wrong) advice. That's why it is important to choose the correct hardware for things like mainsheet controls; it could go way beyond your insurance liability limit if the boom fails and severely injures (or kills) someone. For the extra 2-300 bucks it IS cheap insurance for the long time you will own the boat. It is a small expense relative to the purchase and long-term mainenance and berthing costs; so it should be a no-brainer (IMHO).
Do some online searching for a good price on the hardware; you might find that the cost is not as high as seen on the Harken (MSRP) website should you choose to select items yourself. Garhauer has some pretty good online prices should you decide to go with them.
Call a rigging shop and ask them to spec the correct block setup for your boat. If you do; pay them for their time by purchasing the product through them. That way you can be sure you get the correct size parts; but it will probably cost a bit more than buying online.
I don't know what the load capacity of your old controls are; if you replace them with 4:1 and low load blocks it seems to me like it would be trading one bad apple for another. If those Schaefer blocks happen to be high load carrying you could be making matters worse.
My opinion is based on what the Harken calculator says for 35-45kts. My description of SWL vs. Breaking Load and what it should mean to you is based on my knowledge, experience and judgement as a Mechanical Engineer (FWIW). This is only my opinion; and I don't take any responsibility for your decisions (or anyone else who reads this thread).
Last edited by KeelHaulin; 09-24-2007 at 07:28 PM.