I had the smaller Graupner MiniSpeed, 30-something years ago that was very brisk with a standard 540 motor, x30 or x35 prop and 7.2 volt NiCad buggy pack.
A 550 would have more torque than my 540 and could drive a bigger prop. Also using a LiPo pack would save weight compared with my old boat.
Plenty of motor mount options - MFA do metal ones and there are vac-form and GRP mounts available too. I like the ones that cradle the motor but you may want to add watercooling which could complicate the mount.

Minispeed with standard 540 (Not my boat)

Good morning everyone
I found a Graupner B 28 model as per the pictures attached but without the engine. I thought of using one spare engine of which I also attach photo. I have such motor at home and was used in a model airplane. I ask if from your experience this motor could be good and utilized for the B 28 model. I am not looking for the fast speeds, typical for these models but a speed sufficient just to have fun and of course more than a Krabbe model that i have already. According to my previous mail you can undrstand theat I'm not an expert in boat models and for this reason I'm asking to all of you before to make mistakes. The engine should be a RS 550SW T9 at 12V but my idea is use it at 7,4 Volts with LIPO 2S. My idea if is possible is to avoid to buy a new motor but use this one or a Graupner Speed 500 Race. What is better? In my opinion the RS 550SW motor is better also because the boat data are the following:
Length approx. 950 mm (Around 37 1/2")
Overall length approx. 1050 mm (Around 42")
Width approx. 330 mm (Around 13")
Total weight with RC components approx. 3.2 kg
If i will instal the motor RS 550SW which kind of engine support i need to utilize to fix it inside the model? just a flange infront? or a dobble support (front flange and back side motor support)?
Last matter to develop is the size of ESC, For sure will be an ESC for brushed motor but how many Amperes need to be the ESC? thanks and sorry for all my questions but other way i can not start my new project. Thanks Fulvio