A single 250 was sluggish, and many had issues with being under powered. A single 300 would be better suited, but I am not positive the engine will raise fully with the higher cowling cover, something to look into. The best option for this boat is twin 150's, very economical and added safety of 2 engines. If you never venture more then 5 miles offshore the added engine may not be necessary and sticking with a single might be better for your needs. I have heard good things about the 300 Zuke from owner's I know who have them on other boats, but they are far from speed demons, but they are powerful enough for your needs. Look into where you fish, do you ever venture offshore, do you ever need extra speed, do you fish in an area where bad weather pops up frequently and unannounced, these are all factors for decided between a single and twin. As for going with a twin, 300hp is as low as I would go. Most who own a islander with a single either sold it or repowered it, mostly with twins. My personal choice would be twin F150's for economy and weight, then Zuke 175's or verado 150's(as much as I'm not a merc fan, this engine would suit this boat well...especially the 4 cylinder model), or a single Zuke 300 if going weith singles.