F233 Power question !

[RAKY0311]

I have a formula 233 that I converting to center console and I have the possibility to buy a pair of 115hp optimax engine for a very low price,what do you guys think about that pair for my boat,because the deep v of the 233 I'm going to have problem getting the boat on plane with a low power engine?
Please I need some suggestion in this.
thanks in advance!.

[marshmat]

Hi RAKY,

The specs I found on the Formula 233 indicate roughly the following:
LOA 23'3" 7.1 m
Beam 8'0" 2.44 m
Weight (empty) 5100 lb 2300 kg
Weight (loaded) 7300 lb 3300 kg

(I take it yours is an early to mid '80s model?)

With twin Optimax 115, that's 22 lb/hp empty and 32 lb/hp loaded. A quick guess from Crouch's formula suggests that such a setup would be capable of about 32 knots when empty, more like 26 knots loaded.

I would think you'd want to add a good pair of trim tabs with this setup. Getting the weight balance right will be the tricky part; outboard boats can sometimes have a habit of sitting stern-down compared to their inboard/sterndrive cousins, which can make it harder to climb to plane. But your 115s would likely be lighter than the original engines (260 merc's, according to Formula's literature). In any case, keep a close eye on weight distribution and trim.

[RAKY0311]

thanks Matt for a very detailed explanation,I have a 12" bennett trim tab system for my boat and I build the boat (stringer,transom,floor)with foam and keeping an eye in the weight,please one more question,how will be the predicted performance but in this case with a single 250 Yamaha?,that was my initial choice but now like I say before i have the possibility to buy a low hour 115 opty for $1000 the pair ,but also I concerned about the fuel consumption of 2 engines compared to a single 250,please help me make a decision.

thanks Javier.

[marshmat]

The difference between 230 and 250 hp is not significant enough for an accurate prediction. Without knowing enough about the boat to get anything useful out of a Savitsky or other planing resistance method, the easy way out is Crouch's formula- an empirical method based on general boat type and displacement/power ratio. Not precise or accurate, but it gets you in the general ballpark.

A single will generally be a bit faster and more efficient than twins of similar total power. But if you can get a pair of 115 optimax for a thousand bucks.... (are you serious?????), you just can't beat the price point, even if they do turn out thirstier.

[RAKY0311]

Thanks Matt,yes I'm serius, that's a year 2000 engines,a friend of my are putting a pair of new 150hp and are giving me a help with this price.
Thank you very much for help me,that's what I'm looking for,a general idea in each situation.
Sorry for my poor redaction,English is not my first language,thanks again for an excellent forum!.

Javier.