Naiad Repower 150hp 2-st to 115hp 4-st?

[shuyak]

I am repowering a 6.8m Naiad. It presently has twin '96 Yamaha 150 2-strokes, and will cruise 46mph at 5000rpm. I don't really need the speed, but do appreciate the power when running in heavy seas (saltwater). However, the gas consumption (18gph@4000rpm) and noise is troublesome, and am seriously considering dropping to Yamaha 115's 4-strokes. I am willing to sacrifice some power. It also has a tendency to porpoise when the bow is at all trimmed up, therefore increasing fuel consumption with the bow pushed down so hard. Smaller engines will be 170 lbs lighter and would hopefully trim the boat better. Additionally, I really prefer to stick with Yamahas, and they don't make anything between 115hp & 200hp.<br />The question is, will this turn an otherwise great boat into a dog? The boat weighs wet at 5400#. Anybody got experience here?

 

[MIKE F]

Re: Naiad Repower 150hp 2-st to 115hp 4-st?

Woof,Woof, <br />I think you'd have a dog there Wayne. <br />Since you'd prefer sticking with Yamaha, have you thought about 150HP HPDI's? Seems like they'd be a good replacement, for what you have now.Cheaper than 4 stroke, lighter and should be just as economical as 4Stroke and give better performance.Another good reason for sticking with Yams is the cost involved in re-rigging for other brands.<br />I almost forgot- welcome to the forum <br />

 

[JB]

Re: Naiad Repower 150hp 2-st to 115hp 4-st?

I have a couple of problems with your posts, Guys. <br /><br />Wayne, you say the smaller engines would be 170 # lighter. 150 V6 Yammys weigh about 410#. The F115 weighs about 400#. 17 pounds saving would be closer to it.<br /><br />Mike, what numbers are you using to claim that 150 HPDIs are cheaper and as economical as F115s? I really doubt both claims.<br /><br />Wayne, I would consider the new F225 V6 4 stroke. It weighs 583#, almost 250# less than your two 150 2 strokes or a pair of F115s, and, at about 17 grand, probably cheaper than a pair of either of the above engines.<br /><br />Red sky at night. . .<br />JB

 

[grandx]

Re: Naiad Repower 150hp 2-st to 115hp 4-st?

Wayne, I'm watching this post with you. I also have similair situation. Would like my boat to be lighter in the stern as well. It's tough to find lighter weight options with near equal HP. I'm not ready to repower, hopefully for a while, but have second guessed my last repower more than once. Both the 4 stroke and the direct injection type are heavier than conventional 2 strokes (injection lighter than 4 stroke). The direct injection systems have far greater fuel economy than conventional but I don't know how they compare to 4's, but I'll bet they're close. Single engine option... sure nice to have two out there, especially where you're at. I'd like to see how this ends. Good Luck.

 

[shuyak]

Re: Naiad Repower 150hp 2-st to 115hp 4-st?

Mike, the HDPI 150 is probably the best choice for performance, and I have heard good things about it. The boat is stationed at a remote island in Alaska and all the fuel is hand pumped from barrels--we're getting big arm muscles, but sure would like to cut our costs and effort here...<br />Yes, staying with Yam's saves re-rigging $, plus I really like their quality.<br />Thanks for the welcome.<br /><br />J.B., I re-checked the weights and you are correct in that the combined weight is less than 100# between 115 4st & 150hpdi 2st (I'm not considering the conventional 150). So weight savings isn't going to be a big issue. I have seriously considered the single 225 4st, but my remote operations lend credibility to the redundency/safety considerations of having twins. Plus the added re-fitting considerations to the deep-v hull (longggg shaft & draft) causes me concern. I would likely have to add trim tabs also, as the boat is very trim sensitive on step, and I can now compensate with the twins. <br /><br />I have consulted several local dealers and wrenches, and they seem to think the 115s would perform fine, but--I'd sure like to confirm that before taking the leap...<br /><br />Stay tuned grandx.

 

[MIKE F]

Re: Naiad Repower 150hp 2-st to 115hp 4-st?

JB and Wayne,<br />I apologise, I was making general statements, which I think are true about 4S versus HPDI,if they were the same HP.Unfortunately, I neglected the MINOR fact that Yamaha doesn't make a F150.Must have been a bad night for me. <br />I think the 150 HPDI weights #466 which makes it 60-70# heavier than the F115.

 

[harrison20002]

Re: Naiad Repower 150hp 2-st to 115hp 4-st?

Wayne; I think this may help you make up your mind. In the December issue of Field & Stream, page 42, is an article entitled "The Four Stroke Revolution. It discusses the new VMAX 250, the F200 and the F225 motors along with a couple of others.I thought it was a pretty good article and I'm not in the market for anything that big.<br />Sure hope you can use this and Happy Turkey Day. Hal

 

[suzukidave]

Re: Naiad Repower 150hp 2-st to 115hp 4-st?

Wayne, I've made this suggestion before to people who don't quite need twins and can't quite take the weight, but want the security. There is another option I've seen work well. Get a 225 or whatever will work as a single motor plus a light 40-50 horse 2 stroke (older Yammy?) side by side with dual steering on the transom with the big guy and keep the 50 tilted up most of the time. If you put a very low pitch prop on the 50 it will take you home on plane at maybe 15-20 mph when you need it and it'll be a good trolling motor too. Weight problem solved, you've saved money, you've got security and you might get a fish!

 

[shuyak]

Re: Naiad Repower 150hp 2-st to 115hp 4-st?

Hal & Dave:<br />Thanks for the suggestions. As I understand, using a 225 single would actually provide more power than would appear as there will be only one lower unit dragging through the water. This is tempting, but the reconfiguration of the transom for the deep V hull/longgg shaft makes this a iffy proposition, + I am rather spoiled with twins...but worth considering... Hal, I'll look into that F&S article... Thanks, and Happy Holidays, Wayne