A question about underwater demo charges

[Marc]

Bon dia!

Here I have a question for any of you with some knowledge about explosives.

First a little background. In our last game, the mission assigned to the characters in my pre-Kalisz campaign was to investigate the suspected presence of a handful river barges and two tugs in the old fluvial port of Torun. Once the presence of the barges confirmed, the primary objective was to prevent the barges to flee when elements belonging 5th Infantry Division assaulted the city. The secondary objective was to capture as many of the crewmembers as possible, with the 5th ID HQ thinking about trying to explode the possibility to transport supplies and materials by river, from Chelmno to Włocławek.

Anyway, the solution adopted for one of the groups (I have two groups running simultaneously the same campaign with very different results) was to infiltrate by night to the surrounding high buildings near the port one day before the attack. Once satisfied with the obtained information, two tried to sabotage the barges and tugs setting little demolitions charges to cause easily repairable damages. The charges must detonate little before the first combats in the city, to prevent the crews to have enough time to repair their ships. I have not any knowledge about explosives, so, in a few words, I let them (setting the tasks needed and the difficulty levels), to put little charges underwater one in the rudder of each barge/tug. Each charge was detonated by a timer set on the hull and over the water level. All the process was done by night. So…once the game finished and without taking into account the chances to render useless a barge with this system: 1. Can the normal explosive charge listed in the demo kit be set underwater? 2. Can the connections, the wires and the blasting cap be isolated enough to allow the timer to detonate the underwater charge? Have I allowed them to make an impossible task in the real life? Thanks in advance.