Just want a HF rig in my boat. Have a couple of ICOM's just laying around and and AH-4 tuner collecting dust. The GAM is a quarter wave on 40 meters. As far as options? Wide open to suggestions, have plenty of room 40' boat.
1. A tuned antenna. Mainly, a vertical dipole. Since this is balanced antenna there is no requirement for any additional grounding. Meaning, 100sqft of copper all over the boat. You should be able to run a 40m dipole from the bow or stern to the top of the mast with a spare halyard. Coax cable from the feed point at best possible right angles from the antenna down to the deck. SWR once tuned should get you in the 1.2~1.5 range. No tuner needed.
2. If you do plan on operating on multiple bands for nets or email via Winlink then a random wire antenna is best. The length used by many boaters is 43 feet. That will get you at 1/4λ @ 5.4 MHz. However, with a tuner you can easily work in the 160/80m band. This antenna will tune across the entire HF band. However, there are frequencies that will be 1/2λ that might cause a high impedance. Antenna tuners normally do not like high impedance and will not tune. The minimal would be 23 ft which can easily work 40m on up to 10m. The same applies for 1/2λ frequencies. This antenna will require some grounding. Preferably seawater ground. There is also this device called a KISS-SSB counterpoise. A simple counterpoise that one can build and use. Combine this with seawater ground and you have one hell of a ground plane. For the seawater ground one should use decoupling capacitors to prevent galvanic corrosion.
3. Inverted V with the feed point at the top of the mast. The issue I have with that antenna is the acute angle of less than 45°. This can cause problems. However, some have said it works just fine, but I cannot confirm.
4. 23 ft vertical off the stern. Motor boaters use these. Same grounding and antenna tuner apply.
That's a start for you to digest the possibilities.