Hard or Soft Bimini height

[Rowbert]

I am contemplating a hard Bimini, for the ease of solar panels and overall ease of cleaning, but I don't know how tall to make it. My mainsail is old and needs replaced but still does what I need. My boat is a 1979 John Cherubini 30' Can I assume that the lowest position for the boom would be 90 degrees from the mast, or is there a measurement that I can use?

Second question, would you use stainless or aluminum for the frame? I am a pleasure boater not a racer.

 

[JBP-PA]

Not necessarily 90 degrees, depending on your sail. The only accurate way to know is go sailing, close hauled with the main sheet tight. That should be the lowest point of the boom.
You can, maybe, raise the boom a bit by fudging things. I have a small 4 inch pennant at my mainsail tack to raise it up a bit, but I can only do this because I have extra room at the top and a loose footed main.

 

[Hollyberry]

As JBP says you need to go sailing and make some measurements. However that may well lead to a bimini height that is inconveniently low. Ideally you should have close to standing headroom. Some boats have a two step height, with the higher portion aft of the boom end (depends, of course, on your sailplan and cockpit relationship) Alternately the boom end position may deterimine the fore-and-aft dimension of your bimini.
From the drawing below the helm might have adequate shelter if the entire bimini was aft of the boom end. (In Florida I imagine you're after shade rather than rain protection...) YMMV and it also will depend on whether or not you want to connect to a dodger.

 

[ggrizzard]

My '79 Hunter 30 C came with a 10" +/- slide at the mast at the goose neck
that allows the boom/goose neck to be raised and lowered, depending on the size of the luff of the sail. The original "topping lift" was a fixed wire attached to the back stay
that held the mast in place when the sail was lowered.
Assuming that you don't have an adjustable topping lift, you should get one
for a variety of reasons. Here's two:
1. To hold the boom up to accommodate a bimini of any size.
But, be aware, you may have to adjust the topping lift and the goose neck at
the slide so that your main sail will be the correct shape for sailing.
2. If installed, a full rigged topping lift can be used as a spare main halyard.

If the main sail was replaced by a previous owner, the adjustments are even
more critical for bimini clearance and sail shape.
Send me a PM if you have more questions.
G.

 

[RoyS]

On my similar 1980 H33 I installed a bimini and had to place it aft of the boom end. While this location protects the helmsman it does not shade the forward end of the cockpit. IMHO under no condition do you want to have to crouch under your bimini. I suppose you could raise your boom and modify your mainsail instead.

 

[Rowbert]

Thanks to all for your support. I believe I will attack it from 2 sides, first go for a sail and find the current height and second, decide what I would like for my head clearance. My mast has optional mounting locations for the gooseneck every 2 3/4 inches. I will use the my desired head clearance as the starting point and see what I have to do to make the mainsail higher or get a new one cut to the new measurement. Otherwise I will design the length of the Bimini from the mail sheet to include supports for dingy davits and likely make the frame from aluminum.

 

[Hollyberry]

A bimini frame that will support dinghy davits would need to be a substantial structure... Aluminum would be lighter than SS but not as strong nor as attractive over time.

 

[MikeHoncho]

I would question installing a Bimini forward enough so it have to go under the boom. It will be too low and it’s going to block visibility of the rigging.