I've bought a fishfinder for depth measurements and have been really happy with it... Mine is a simple hummingbird unit with tri-band sonar. It gets really accurate bottom readings and graphic display is easy to keep track of depth readings to use with charts... I wouldn't recommend combo units since if the unit fails you have none of the tools, individual units are better... Handheld GPS wise if you have a data cord input/output you can use e-charts on your computer or connect it to your VHF to get lang/long info on your VHF and send DSC signal with your location...
Quick tip: If you install the transducent to your rudder instead of the hull you will avoid another hole to create problems and can get readings wider than fixed installation. My transducent is installed on the back of the rudder and I can get readings of the wider area beneath the boat by turning the rudder left and right...
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Materialism: Buying the things we don't need, with money we don't have, to impress people who don't matter.