Not for mom or kids. Jolts from the boat, dirty water, excessive sun and heat can be dangerous whether a person is pregnant or not. There are safer ways to enjoy nature when "with child" or with family!
No. I would not risk the pregnancy. If something was to happen there could be alot of unnecessary guilt.
Avoid. Many activities are safe in pregnancy but in general you want to avoid activities that cause trauma or jarring to the uterus. High speed boating is similar to rollercoasters. There is lots of bouncing, quick turns and quick starts and stops. This would not be safe activity for pregnancy.