Post Number: 1
|Posted on Thursday, September 21, 2006 - 10:43 am: ||
I would be most grateful for any advice on the correct sizing of engine for a 18 foot Thames riverboat boat I'm refurbishing. It has the remains of a R3M (all top end missing) so no salvaging here! I suspect that the 1.5 hp may have been a little light and I will be adding quite some weight to the boat and wondered if I could replace with the more powerful P5M. This would mean increasing the prop size a tad. But can anyone give me an opinion on:
1) Are the two engines of similar dimensions?
2) Bearing in mind I am never likely to want to go more than a leisurly 5 knotts is my assesment correct about engine size ( I do know that there are loads of scientific calculations to determine engine size, but hey if it's overpowered just means higher fuel bills!)?
3) Would it be foolishness to use the bigger engine and prop configuration with the lighter existing (R3M) prop shaft - I am not up to renewing the prop shaft and stern tube) or would it result in the prop shaft doing something bad?
4) All other things being equal is one of the two engines better in any way from the other; reliability, starting routine maintenance etc.
I would really appreciate your views. I will be refurbishing a R3M or P5M one or 'tother!
Post Number: 4
|Posted on Friday, September 22, 2006 - 04:06 pm: ||
R3M's are great for this type of river launch work - their more efficient 1000 rpm prop means they can drive larger hulls than their R3MC stablemate.
However, if you're adding a significant amount of weight, then the P5M might be the way to go - Stuart quote an 18' long x 5'6" beam x 1'6" draft P5MA powered launch achieving 5.2 knots. Bear in mind that the P5M is heavier than the R3M (195 lbs vs. 125 lbs), larger (22" loa x 14.5" wide vs ~ 18" x ~ 11"); the R3M & P5MA props are the same dia (10"), but the P5MA prop is an inch finer in pitch.
I must confess, my money would be on retaining the R3M...
Post Number: 2
|Posted on Sunday, September 24, 2006 - 02:58 am: ||
Many thanks for this. I must say I really wanted to hear that the R3M would be the way to go. I have the chance of rescuing a 1949 model that is ripe for rebuilding and was rellishing the prospect!