Like a TARDIS, the boat's cabin inside is larger than the boat is outside.
During Burger's direct examination of Lt. Tragg regarding the ax, Perry can be seen in the background looking to his left. But the next shot is a closeup of Perry, and he's looking toward Burger.
Perry called the gruff Old Captain to the stand, but after his direct testimony was concluded, the Judge released him without giving Prosecutor Burger the opportunity to cross-examine him.
Perry and Della spend the night in the lower level of a boat, supposedly alone. But when Della climbs the ladder to the deck to leave the boat, with Perry still waiting below, she can be heard to say softly to someone above, "Excuse me."
The victim is murdered with a blow on top of the head with a hand axe. When the body is discovered, there is no blood on top of the victim's head; his hair isn't even mussed.
Martha Bradford and Jack Harper both handle some candles found at the murder scene, but Martha's fingerprints are the only ones recovered by the police.
After Bradford is found murdered on his sailboat, the police would not have left the boat in the middle of the harbor; they would have impounded the boat as evidence. Several characters access the boat in the harbor after the murder is discovered, when it should have been in the impound yard.
After finding out why the candle was crooked, Perry and Della exit the boat, but, they leave the candle burning.
When asked by Perry to confirm the time of low tide on a specific date, Captain Noble consults a tide chart he had been carrying in his pocket. The judge should have made a comment to this effect for the court transcript, but failed to do so.
After Perry and Della discover the body, Perry uses a handkerchief to pick up the candle holder to avoid leaving fingerprints, but Della leans on the table with bare hands. Thus, her fingerprints would be on the table's edge.