I am putting a stereo in the boat. it is only 60watts x 4, so 15 watts per channel right? the speaker specs are

• 200 Watts Power (PMPO)
• 100 Watts Power (RMS)
• Frequency Response: 45-20,000Hz
• Sensitivity: 90dB • Rubber Surround IMPP Cone
• Soft Dome Diaphragm High Performance Tweeter
• Mounting Depth: 70mm (2.75")
• 15Oz Magnet

I wanted to add an amp also. given this info i dont think it makes sense to put in anything more than a 200 watt amp. here is the spec on the amp i was thinking about.

• 200 watts x 2 output, 400 watts x 1 bridged output
• High/Low level input
• Remote turn On/Off • Variable input gain
• Thermal
• Overload, Short Circuit Protection

there are only 2 speakers in the boat. think it will be sufficient?

Many times the wording is vague on output claims, but as you typed it means 60w per channel.
Your speakers are rated at 100w RMS, which is fine for the output of the rated head unit.

Adding an outboard amp, those 100w rated speakers will burn once you crank up the bass. The voice coil wire is fine guage-enamel coated and they heat up and melt, in return causing the speaker diaphram to stick. That causes the "crackling" sound on blown speakers....

I would try it without the amp, you will get plenty of volume as is.

Speaker input tolerance claims are suspect with cheap speakers, make sure they are a good marine application brand