hi, I have a 27 express cruiser, not sure if your boat is the same, I removed the twin gas engines and installed a cummins / dodge 6bt in it, did the marine conversion myself and tweeked the pump a bit so I might be in the 250 to 300 hp range. it will do 20 knots, I cruise between 8 and 9 knots at 1400 rpm and about 2.5gph, headed down to the sea of cortez this afternoon for 10 days island hopping trip...im sure that if I cruised 7 knots I would easily get 2gph.. regarding your present set up and speed, anytime you ask the boat to go over its designed hull speed, in our case about 7 knots, your fuel requirements go up drastically, nothing you can do about it...! it sounds like you are propped right as it is if you can just reach red line at wide open throttle, the only "sure" way to increase efficiency is to spin a larger, slower turning prop, but that means different gear ratio, you would gain hull speed fuel efficiency but loose some high speed efficiency... im running a 19X21 prop right now. Eric----- Original Message ----- From: dodgetkboy78<mailto:[email protected]> To: UnifliteWorld<mailto:[email protected]> Sent: Thursday, September 10, 2009 11:01 PM Subject: [UnifliteWorld] Prop pitch, GPH, cruising speed, RPM
I have recently bought a 1970 hardtop express. It is registered as a 28', 9'8" beam boat, from what I can tell, it is a 27'3" boat. But thats not the question. It came with a 225hp 318, and recently has had an update to a 360. The transmission, prop, ect, was all left alone. Top speed, if you got the guts to rev it that high, is around 24kts, at 5100rpm. Yeah, ouch. To stay on step, it takes 3300rpm, at about 13kts. I have been cruising at 7-8kts, at 1800-2000rpm. Throttle is barley open, and it burns around 4GPH at this speed. Here is my question. Does that sound right? It takes the 4bbls open a bit to keep it at 13kts. I just cant bring myself to run it that hard, for long periods of time. Could I pitch the prop to make it cruise better at 12-13kts? Or would it just take more throttle at less RPM? Either way, the 360 almost seems to big/too little. I can be happy with it at 7-8kts, but was wondering if it was, well, normal. Other than that, this is the nicest handling, roomy, well built, smooth riding boat I coould ever imagine, takes 4' following chop like a champ, turns on a dime, and has a real "Heavy" safe feeling in the water. My plans are to put a 330hp cummins in it eventually, that should push it 15kts, and burn the same as the 360 at 8 I bet, but for right now, I want to get the most out of my 360. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "UnifliteWorld" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/unifliteworld?hl=en -~----------~----~----~----~------~----~------~--~---
