[Sailor Steve]

I think I may have found it. Go into SH4's Data folder and open the Sea folder. Right near the top you'll find NLifeboat_01 and NLifeboat_02.

Open the Cfg file for NLifeboat_01 and you'll see the following:

[Unit]
ClassName=LifeboatSmall
3DModelFileName=data/Sea/NLifeboat_01/NLifeBoat_01
UnitType=105
MaxSpeed=2
Length=4.8
Width=2.8
Mast=1
Draft=0.2
Displacement=0.3
DisplacementVariation=0
RenownAwarded=0
CrewComplement=4
SurvivalRate=0
SurvivalPercentage=60
[Loadout 1]
Name=Axis
Type=0
[Loadout 2]
Name=Allied
Type=0

I highlighted the relevant lines. The displacement looks fine. If you want to get some credit for sinking them, change RenownAwarded to a positive value. If you want to be punished add a negative value, say -5 (or -500 if you're serious about it being a war crime).

I'm not 100% certain about it, but if it doesn't work you can always change it back to zero.

NLifeboat_02 is the same, but the Displacement is 1. The adjustment to the RenownAwarded line is the same.